[fulk]

There's a module-variable that is controlling the head-slave's actions... for some reason, when i entered the illithid map it was already set to '1', meaning that I've pissed the guy off...

I think it must be a bug, here's how you can get around it:

Enter debug mode:
> DebugMode 1

Update the module-variable:
> dm_setmodulevarint X2_Q2DGladsAttackedInPens 0

Open the door to the pen, pause the game, enter the following command and target the leader (only hostile character):
> dm_setfactiondefender

Now he should turn friendly, and you can free him and the slaves. Remember to kill everyone in the city..