In a multiplayer game, on a small map, at the highest difficulty level, Demons consistently lose to Necromancers, Humans, and the Fortress, who tank and tear through all encountered neutral creatures indiscriminately. The lack of healing spells is a factor. It's practically impossible to acquire monsters of level 4-7 in the first week without any losses.

Gentlemen, I'm curious to know if there are ways to compensate for the disadvantage in the first week? Or are there any combat tactics for the first week?

I played the first level of the campaign without healing spells.
There are tactics. I'll write them for the Warrior. For the Mage, everything is clear; you can go into Earth and Darkness.
1) Reinforcements. This is obvious.
1a) Matrons have auto-reinforcements :)
2) Drain. This is also clear, I think. But the Warrior has little mana, so use it in emergencies.
3) Stacks of 1 unit to cover the main stacks and absorb retaliatory attacks.

Oh! And now I'm thinking, if this single unit is a Lilim, then during a retaliatory attack, enemies take reflected damage. How much is reflected? It doesn't seem to depend on the stack size, right? Or the classic - single units as berserkers. By absorbing the retaliatory attack, they reduce the damage of enemy stacks. The effect seems to last until the end of the battle.

4) The Lilim's charm ability.

Save the dogs, just in case. And the Sadists. They are the main attackers. In general, it's all like in the fifth game; the price of any mistake in battle is incredibly high for Inferno, and there will be no chance to correct it.

Added 4 minutes ago

It's strange how they made the Demons, if you look closely.
It feels like they just used the "leftovers" for them. Humans - morale and light, Necromancers - darkness and corpses, Nagas - water and attacks on different targets, Orcs - just attacks, I forgot. But for Demons, they crammed in fire and luck)))

It seems to me that at level 15, the Inferno Fighter becomes very dangerous, especially with the right combat perks. However, the level of danger is directly proportional to the amount of "meat" preserved during previous development :)

Added 2 minutes ago

The thing is that Lilim will not enhance the Fighter well, because its growth is more in physical defense and attack.

On the other hand, you don't have to worry about whether or not to take perks for ranged attacks