Added 9 minutes later
I also restarted the final stage twice. When asked if I was ready to fight Markel, he immediately attacked all three of us. By that point, Faidaen's army was not very good, and he was killed. The second time, I tried a different approach. Markel attacks everyone, regardless of where they are at that moment! I tried this: I sent Godric and Faidaen to the farthest Castles, where about 20-30 angels had already gathered. And they stayed there until the last minute, reinforcing themselves with all the available resources. The mage went to the enemy territory in the lower left corner and could pull reinforcements from the lower left Castle from there. There weren't any angels there yet, but the rest were enough. Then, I attacked the Castle with the mage, and Markel attacked everyone else. But they already had substantial armies, and they won!