Auto-translated
If you're running out of steam, reduce the difficulty. The strategy is to defeat everyone. The first target is the red faction. Then, I left a supporting hero to guard the passage to my two castles, while the main hero went to capture the enemy castles.
Malassa's daughter must always be with the main hero. If she dies or is transferred to another hero or left in a town, the mission will fail immediately.
Although I played through the campaigns of this expansion pack not too long ago, I remember the original campaigns better. I completed them very quickly and easily (all on the first attempt). Only the last mission presented some minor problems. But, even if I hadn't completed it on the first attempt, I would have easily completed it on the second. I played as a Warrior because I wanted to finish them quickly and buy the second expansion pack.