Playing on Medium difficulty with the IWD NPC pack, Unfinished Business and Fix Pack. Party is composed of:

Level 6 Sword & Shield Fighter AC 0, THAC0 8
Level 6 2-Handed Sword Paladin AC 2, THAC0 11
Level 5/5 Hammer/Flail Ranger/Cleric AC 0, THAC0 13
Level 5/5 Mace Figher/Cleric AC 2, THAC0 13
Level 6/5 Short Bow Thief/Mage AC 4, THAC0 16 - Has Haste
Level 6 Mage AC 5, THAC0 16 - Has 2 Fireballs

Up until this point, I really haven't had much of a problem. I frequently make use of luring enemies out 1 at a time to slaughter. For this fight, that doesn't work; luring the top most troll just invites everyone else. I figure I can use undead minions to absorb the priests' spells so they can't be used on my party but even then, the 7 or 8 trolls are too much. You could probably take out the priests entirely and the trolls alone would wreck my team. About the only thing I know that might help are Chromatic Orbs that can successfully stun them, not to mention I need to kill them with fire (which requires evacuating my melee characters out of range) when they're nearly dead. Perhaps going to far side of the map might stagger some of them so they arrive slower? I'd rather not change the difficulty. Any advice?

Hmph. I searched for "Dragon's Eye" before I made this and again when I read this again but got no results. Subsequent searchs now show results. Bah. Anyway...

It didn't cover much that could apply to me since I had no druid. Haste + Bless on party and 6 undead minions, various buffing potions, sending in the undead to attract everyone, using ranged weapons on the priests, Protection from Evil AC bonus for melee fighters, Fireballs towards the undead group and mopping up the rest with Burning Hands and some 2nd level Scorcher spell when the trolls were "dead" proved effective the 1st time I tried it. Suprisingly only lost about 40 HP total in the fight.

I had great difficulties with this too. Tried to lure them out into a skull trap in that narrow corridor or further back, tried to lure them out one at a time, but like you say the whole lot comes after you. After dying 7-8 times, mainly from that damn hold person thing, which prevents us from retreating as the held persons would quickly die, I gave up and went to the potions pack. Dwarf shield and axe fighter got our only potion of freedom and glugged our only potion of speed, and went back and ran around for a bit (finally I could see what and who were actually there), which prompted the priests to hail him with hold spells. None of it took now, and I then ran him way back to where the party was. When we finally managed to take out the priests, the battle was in reality won. With nothing bar a 50% fire sword to kill trolls with it took a while, but we finally managed to kill them all.

Very tough fight in the best of times, and without a good selection of spells it's even worse. Now I'm struggling with another party of priests further down, but now I don't have potion of freedom to help us out. This game is tough as nails - way more difficult than Baldur's Gate. Fun challenge though.

How many preparations of that spell do they *have?!*

It's an optional battle so you can avoid this part of the map for now and explore one level below first to get more XP and better equipment. Trolls do slashing damage so wearing plate (which grants additional +3 vs slashing) is helpful.

If you're desperate you can try resting and fighting interrupting monsters for farming XP.

Summon some skeletons with your priest. then cast stinking cloud (undead are immune) You can also set up some skull traps with one of your mages. toss in some fireballs to finish them off. Use direct damage spells and ranged attacks while the enemies are occupied by the skeletons and stinking cloud.

As somebody else already mentioned, you can skip this fight for now and come back later when you're stronger.

If you're able, give a tank immunity to Hold Person and have them hold the choke point in the narrow passageway. Once the priests run out of Hold Person spells, bring in everybody else and clean up.

I took out many trolls with multiple Aganazzar's Scorcher spells. Think of it as a flaming laser beam that does persistent damage to anything that gets in the way. SO... as the trolls first aggro and come around the NW corner of the cave, they are all in single file. Target the rearmost troll with the scorcher, and you hit all of them. As the trolls move around. you can reposition your caster so that the laser beam hits multiple targets. The trolls will move up and engage your tanky fighters, so the MU needs to stay mobile and flank the trolls to avoid friendly fire. But if done right, you can usually get quite high flame damage against 5-6 trolls at a time.

Also the flaming potions that you collected from the lizard men on lvl 1 in Dragons eye are quite useful to do AoE damage on the trolls. The gnome in the flying ship back in Kuldahar sells flaming oil too.

To finish off any trolls that have fallen unconscious but are regenerating, use Burning Hands.

Target enemy spellcasters with arrow fire spam. If they get shot, it interrupts their spell casting.