P.S. I'm tired of making excuses, but if after these explanations you still insist on your version—I will remove the additions and only correct punctuation and spelling... As for what meaning or essence your book will have, that will no longer be my concern. And I couldn't care less...
In general, I just wanted to help, but since you don't want to... well, fine!

Colleague, there is no need to take the authors' words so personally. Everyone wants to keep their own version; that's only natural. But you are absolutely right in pointing out factual errors. That is precisely what a proofreader's job consists of in this case. Separately to the authors—do not insist on your version if factual errors are evident. Colleague Simas is pointing them out correctly. Also, the battle scene, it seems to me, comes too early. It turns out we throw the reader into a whirlwind of events without giving them time to understand what the work is actually about.

Added after 3 minutes
Now I want to present my version of the backstory.
High Archmage Letius Calgius, despite his venerable age, almost ran down the corridor of the Spell Chamber. His servants, first- and second-year acolytes, could barely keep up with their teacher, being in complete confusion over this haste of the universally respected gentleman, one of the Pillars of the powerful Order of Guardians. The venerable elder, who usually walked majestically through the halls of the Great Magic Academy in his crimson and gold robe, wearing an unchanging fur mitre richly adorned with gold and precious stones, holding his carved Staff of Higher Initiation in his hand, always surrounded by his assistants and master mages, was now rushing, apparently despite severe pain in his elderly joints. Approaching the door of the Council Chamber with a lumbering gait, Messire Archmage carelessly waved his staff, and the door swung open before him—as it seemed to the surrounding mages and acolytes, obsequiously and respectfully. The Archmage stumbled into the chamber, and behind his back, immediately cutting off the gazes of the curious and the magical attempts of the particularly bold, the door slammed shut and seemed to become one with the wall. Those remaining knew: only someone from the Pillars of the Order of Guardians could enter this hall, but certainly not outsiders, even if they imagined themselves powerful mages and believed they were on first-name terms with Messire Dean of the renowned Magic Academy.
The Archmage, having run into the Council Chamber, collapsed into a luxurious chair, trying to catch his breath and coughing, holding his chest with an elderly hand. If not for the message brought twenty minutes ago by a postal dragonet of the Sylvan elves to his private quarters, calling him immediately due to very important and serious circumstances to visit the Council Chamber, would he have allowed himself, in his advanced years, to hop about like a mischievous boy before his students and colleagues—many of whom also once graduated from this Academy in his faculty—while rushing here? But such requests from his brethren, the Pillars of the Order of Guardians, were extremely rare and concerned only very important and serious events occurring on Drakodar (currently a working title for the world proposed by colleague Dragon Mallassy—apparently, kinship requires it).
Having caught his breath slightly, Letius Calgius concentrated, recalled the corresponding materialization formula, and spoke it. A three-legged marble table with a polished top covered in natural patterns appeared in the room. On the marble surface of the table rested a crystal ball on a stand that a skilled master had carved in the form of a man with a drawn sword, an elf with a taut bow, and a dwarf with a raised hammer. The surface of the sphere shimmered with lights, reflecting the astral world that permeates the real world. By waving his staff in the air and uttering another spell, the Archmage caused the magnificent and elegant lamps hanging here and there on the walls of the Chamber to go out. Since outsiders were forbidden entry, all daily work was performed by the master's magic; therefore, all furniture in the Chamber was arranged according to the wishes of the Archmage, who in his best years was not known for neatness, always justifying his shortcomings with a creative flight of thought.
The Archmage placed his hands on the piercingly cold Summoning ball and, mentally straining, sent a spell into the astral plane calling all Pillars to create a Council Circle.
Although the Summoning ball was physically present in this world, it refracted the astral within itself, and the surface of the sphere never heated up. Every time after a communication session, the Archmage suffered from joints aching with arthritis. It was fortunate that such councils were very rare.
Leaning back against the chair but keeping his hands on the ball and waiting for his interlocutors, the Archmage mentally sifted through the reasons that had prompted his forest brother to send a messenger dragon. None of the events that had occurred recently and were known to Letius Calgius required an urgent convening of the Council.
But then an image appeared in the Archmage's mind of Trent, one of the Pillars of the Order, a Dark Elf by race. His mental image was an exact projection of the real one, and in the real world, his beautiful but unfamiliar face to human eyes was always stern and gloomy.
"Did you call, brother?"—the Dark Elf's question arose in the Archmage's head.
"Yes, brother. Our Hilael has very important information."—Trent's face twisted in a spasm. The Archmage knew how much these elves hated each other, although they belonged to the same species, they were completely different in internal nature.
"So important that he decided to convene the Council? And you agreed? What could that herbalist possibly have that is important? No doubt he'll be screaming again about an invasion of his beloved forests!"—the Dark one asked fiercely. Although nuances are not supposed to be transmitted in a mental conversation, the Archmage caught a storm of hatred in Trent's soul.
"Brother, do not get heated,"—the Archmage tried to calm the Dark one. "Our forest brother has no need to involve himself in earthly conflicts. If he asks the Council to gather, then he truly has important information."
At this time, the image of a third interlocutor appeared on the astral plane: Trogg, a dwarf by origin.
"What happened, brothers?"—the dwarf asked. It seemed that the astral shuddered from the booming bass, although everyone knew that tones of voice are not transmitted in the mental plane, but the Pillars knew their most powerful mage among them, the dwarven one, well enough. "What is the Council about?"
"Another bug died for our Hilael!"—Trent added sarcastically.
"Be fair, brother,"—Letius Calgius requested. "Trogg, Hilael asked to convene the Council to report something extremely important."
"What could be more important than Fire Rats?"—the dwarf responded irritably. "They are eating our fortifications and the mines are collapsing."
"Not surprising,"—Trent replied snidely, "your guards got drunk again, so they pee wherever they want, and the supports rot."
The Archmage warily waited for an explosion from the unrestrained dwarf, but he apparently decided that it was easier to kill the Dark one physically than to change him, and remained silent. After a short mutual silence, Trent said: "If this creature doesn't make contact now..."
As if responding to some spell, the image of the High Elf Hilael appeared in the mental field, but in what state! His hair, usually extremely neatly arranged and tied with colored straps, was disheveled and partially singed; his forehead and right cheek were burned, and blood flowed down his chin from a scratched left cheek.
But the thought-voice of the refined elf was, as always, full of dignity:
"Forgive me, brothers, but the delay was not caused by me. A battle recently took place around my hut!"
All the mages froze; only the Dark one looked at his rival with a satisfied smirk.
The Pillars of the Order of Guardians knew that Hilael called a luxurious tree palace "hut," created atop a majestic ash surrounded by powerful charms. Simply approaching the ash was very difficult even for a powerful wizard, especially considering that the ash was located deep within the Enchanted Ancient Forest, where nothing and no one could hide from the keen eyes of elven rangers. Thus, what the elven mage said was unrealistic, but no one would suspect their brother of a hoax. Everyone knew Hilael as a very rational elf who, even in everyday life, would never allow himself to be even slightly unserious. Therefore, all the astrally present mages felt that something incomprehensible and therefore very dangerous had happened.
Hilael continued: "It all began at dawn. I detected something—a fluctuation in the general tension of the world's magical component. Deciding to analyze this phenomenon, which quickly faded after a sudden surge, I discovered that this surge was produced by some powerful artifact of local significance. Through a Search spell, I found the center of this surge and... brace yourselves, brothers... these were residual fluctuations of the power of the Amulet of Hell, parts of which we all keep. I immediately tried to reach Agremay, who keeps that part, and simultaneously sent a forest dragonet with a message to Letius. I did not feel Agremay, and that means only one thing: he did not want to communicate..."
"...Or he was dead!"—the Dark one interrupted.
"Do not talk nonsense, brother,"—Hilael showered him with contempt, "the death of any of us would be felt by all others instantly. Agremay is alive; for some reason he used the Amulet, and soon after that an attack on our forest began. I was warned by the secrets of our scouts that several zombies tried to penetrate the forest. They were destroyed quite quickly, but then a cloud of Death struck the scouts who had revealed themselves. Several scouts died. Druids were summoned and word was sent to me. And then a real battle broke out. From the northern edge of the forest, where we keep no main troops other than scout secrets, undead of all kinds advanced. I was urgently summoned as the nearest and strongest of mages, and now reinforcements from other parts of the forest are moving toward us. We repelled the attack, although I cannot guarantee it will not happen again, but the very fact of an undead attack and Agremay's stubborn silence speaks volumes. We all know about the increasing attempts by demons to penetrate our world again, and today's incident may not be accidental. As regrettable as it is, brothers, it seems Agremay is a traitor. Lately he has leaned toward the Cult of Death, and the undead attack—are these not links in one chain? Especially if this is a provocation by demons. Then everything is very bad..."
"If you are right, brother,"—the Archmage wove his thought slowly and deliberately, "then it's not just bad, it's a catastrophe. If Agremay, one of us, is a traitor and the undead attack was his doing with the help of the Amulet of Hell, then... Then he knows where the other parts of the Soul Talisman are located. We all know perfectly well that Hell craves this Talisman to bring back into the world the one who was exiled. If Hell obtains this Talisman, the lords of Inferno will find the body and give it to the Disembodied. Our races are strong now, but strong individually. Our enemies will not let us unite again, and demons allied with the undead will crush us one by one. Speak, brothers..."
"I don't believe the forester's words,"—Trent said thoughtfully, "but his appearance... I believe that even if the flower-grower tells a quarter of the truth, we must re-hide the parts of the composite Talisman."
The ending is not yet developed; waiting for reviews on the proposed piece.

Added after 10 minutes

Esteemed colleagues! If we are composing a literary work, that's normal.
In general, I haven't fully grasped what exactly is being planned here.

Colleague, as I understand it, you have already had the opportunity to encounter a scenario, and you know that first comes the composition of a literary work, and then a scenario is created based on it. In our group, things are progressing exactly this way. We are creating an epic work, and then, as soon as it is finished, we will try to fulfill the function of a scenario, and I think your help will be invaluable. I would separately ask you to post YOUR versions of the plot for the demons, and we will try to evaluate them and make adjustments.

Added after 30 minutes

And also:
1. Zeratul inserted your text, slightly corrected the clothing and gait.
.

Colleague, I am grateful for the editing, but I didn't mention the clothing without reason. It would be strange if a great mage, one of the deans, walked around in a simple gray robe. A robe is called a robe because it differs from everyday clothes, intended only for formal appearances. In this case, it's like a guild sign or at least a faculty mark—something like a special forces uniform or an assassin's camouflage cloak