I forget the names - this is the main floor of moonrise boss?
If so here's what I did - siding with harpers (and I had to reload many times).
1. Recruit Jaheria - otherwise she Leroy Jenkins her way into the battle
2. I still had a haste spore thingy. I made a cloud of haste spores so harpers and party were hasted and I ran back into the cloud when the haste ran you
3. Wizard Tav - I was counterspelling most of the time.
4. Shadowheart - silence, healing.
5. Jaheria - ice storm, ice storm, panther
6. Wyll - who I made into a thief - using wyvern poison, disrupting the warlocks.
7. Karlach - smash
And I didn't do this because I have an irrational dislike of surfaces after playing DOS 2 but DOS tactics might work here as well. Ice storm, follow with fireball and then electrify the floor. That will keep the warlocks distracted while you take out the true souls.
