I played the Original BGII many times and this is one of many quests I know I have done in the past, so I know how its supposed to go.
This is related to the quest from Aerie's Uncle Quayle who asks me to help some friends of his.
What I did was I rescued Haer'Dalis before I spoke to the people in the Five Flagons inn who needed help.
I returned there after rescuing Haer'Dalis, and gave them the planar stone.
At this point I agree to defend them while they search for the right astral conduit.
After a few waves of monsters, this is during a clam between 2 waves, Haer'Dalis suddenly screams out "No! The troupe... My Friends! NO!" and then the whole troupe becomes hostile and attacks me.
It happens every time as the same point, I have tried 5 times now. and I have done absolutely nothing that should have provoked that reaction.
If I had attacked anyone in the troupe I could understand it, but I have not done anything whatsoever except attacking the monsters coming out of the portal.
I suspect that rescuing Haer'Dalis before speaking to the troupe at the Five Flagons may have resulted in this happening, but regardless of what the reason are, I am unable to continue this quest-line due to this.
Edit: Some more details after yet another failed attempt
1. The sudden turning of the troupe happens after the 3rd wave of monsters, after some shadow fiends attacks.
2. AOE spells have nothing to do with the sudden turning I cast multiple of them that did not affect the troupe.
3. I have no mods installed, its the vanilla version of the game I'm playing.
I do have a savegame from right before this happens if that will help with the troubleshooting.
All I need is to know where the savegames are located and I can provide it.