Two sisters.

I'm not an expert, but it seems to me that the scenario could have been made more dynamic by having one exit from the dungeon that is initially closed and guarded by a quest-related keyholder (like in Heroes 4, I'm not sure about Heroes 5). This exit could open after the deaths of Rolf, Wulfsten, and that nasty one-eyed creature, and then the mission would end after killing the king and capturing the capital.
On one hand, this would make the scenario less hardcore, but on the other hand, it would also make it less frustrating and more predictable. As practice has shown, there's nothing more unpleasant than running around the entire map chasing a lone hero against whom you can't properly defend yourself with single or double unit reinforcements in castles.