Then abandon this quest. The reward isn't worth it.
It's better to continue with the main storyline – there are NO bugs in it.

Added 8 minutes later
Ah, I understand what the problem is. There's a hard dependency in the script, not only on 20 Druids, but also on one quest.
Did you take the quest from the Elder Druids near Shellera? Because it's absolutely necessary for the Ents to join.

I don't know what Shellera is; I probably didn't take that quest. To make it easier to complete the 3 final battles, it would be possible to add a turn skip between them, because otherwise you have to split the army between two heroes, and it's impossible to rearrange artifacts. Overall, the map is great; there are many new units and buildings that I really liked. Dominic's special ability is very cool, and the second main hero's (Letos's) special ability is decent in the first 4-5 weeks, but then it's not so good. Plague doesn't deal as much damage anymore, especially since all the bosses have Darkness Ward, so by the end of the game, you can say the special ability is practically useless. On this difficulty, the hero is quite manageable; it took 139 days, most of which were spent leveling up troops in the fortress. The build is simple: light, darkness, defense, attack, magic. It's unclear why the author only gave 3 heroes for such a large map.
Looking forward to the sequel!!
Ps: If anyone plays it, it might be helpful to know that you can remove mind control not only with Amnesia and Remove Curse, but also with Vampirism.