Try to kill Kaga and the druids before raiding the grove; then the tieflings will help to defeat them, and there will be no problem
I did so, in the process the tiefling leader died. And then I just killed the guards at the gate and broke the gate, and went to the camp. I didn't even have a battle scene, when I came to the grove everyone was already dead, and they congratulated me on my victory.
This is an early access flaw, but this way you can complete the quest
