Okay, here's how it goes. Make one of the heroes your main hero – upgrade the Spearman building in the town – gather your troops – hire caravans. With your second hero, take two peasant huts – on the second (or third) day, venture out.
For the first two weeks, completely clear the territory, avoiding particularly difficult monsters. The second hero gathers resources for the first, carries unnecessary artifacts to the town, and exchanges them for gold. Build up the town to the Inquisitors level, and be sure to build a Capitol. You can do this by the second week. If you're lucky, you can even build Knights.
By the end of the first month, be sure to clear the graveyard and gather your forces in the town. Summon caravans – complete two quests – receive reinforcements. Gather the entire army together, finish off all the monsters. Finish building up the town with the remaining resources.
1.5-2 months. Attack the Undead at the graveyard and get the Tome of Darkness. Then you can have some fun with the Dwarf outpost. But it's better to defeat the Necromancer first – you'll collect the entire set of Lion artifacts by completing the quest, and the help of Archangels and Inquisitors won't be superfluous. Gather in the town one last time, summon caravans, and upgrade your troops.
Decide whether to go to war with two heroes or one. Take the first and second Dwarf towns, depending on the situation.
After that, anything can happen. Most likely, you'll encounter a fairly powerful Dwarf, but you can definitely defeat him.
1) Use mass Light spells – it's best to use Stone Skin and Dodge – buff your troops. Use Inquisitors to cast Prophecy on the Archers. It's also best to cast Haste beforehand. Shoot down the most dangerous units in the enemy army; it's better not to rush in, as the Haven army is strong in defense.
2) Equip the Tome of Darkness – start messing with the enemies, but it's still best to use Haste beforehand, and use Inquisitors to cast Prophecy on the Archers. The battles will be quite easy.
3) Stay in the captured castles. Enemies can only reach you with Erls (Jarls, etc.); destroy them with Pikemen, and then with Catapults. You can level up the siege machines with a triple fire ballista, and if you're lucky with the Ring of the Magi..., it will simply cut down Dwarves, maybe even distract them.
Thus, gradually advance through the lands of the Dwarves. There will only be two difficulties there – multi-turn portals and enemies coming from everywhere, and, of course, Rolf. He's a real cheater. You'll need to use all your abilities against him. You can try to repel his attack in the town.
After Rolf is defeated, everything becomes easy and simple. Well, defeating Wulstan and Hangwul in their towns is not an impossible task.
Something like that.

The second hero gathers resources for the first, carries unnecessary artifacts to the town, and exchanges them for gold.