Fighting the luremaster...

[enrirex]

That's it. I have solved the riddles, explored the mansion and the dungeon and activated the portal. But now I'm stuck in the middle of the battle against the Luremaster itself; he revealed himself as a quite challenging foe, more challenging than I thought.
The real problem is not defeating him, is to defeat him with all my party members ALIVE! Usually, enemies focus their attacks against the weakest member, the bard. Even if I protect her (she is a female) with all my might, then another member falls, usually hit by Finger of Death.
Since this is my 8th attempt (Beliphet died in my second try with all the members alive, strange isn't it?) I'm starting to think a new strategy. My previous methods developed were:

Chase the luremaster: Simple. I cast every defensive and useful spell before entering in the portal (Haste, Tenser's transformation and Seven Eyes in particular), then I just click on the luremaster, damage him, using cure spells when someone is going to die and Haste again if someone dispels it. But this just doesn't work, when I stop my assault I get attacked by any spirit in the arena. Since this didn't work, I developed the…

…Death to the heroes: After casting the previous spell, I concentrate every party member against one enemy, while my bard support the team with her song and occasionally damage with offensive spell. If someone gets to her, I direct a strong character against them and - while he distracts the enemy - I use dimensional door. That's it. The problem is that the heroes don't easily fall. I can't choose which enemy kill first, though.
If I attack clerics, mages destroy a party member with Finger of Death
If I attack mages, clerics use dispel on me
If I attack warriors, a gentle cloaked skeleton armed with a huge scythe brings my party sex feet under ground

Since my party is characterized mostly with fighting power (one Paladin, a Fighter, a Fighter/mage, a Cleric/Ranger, a Rogue/Fighter and my splendid Bard) I'm lacking in magical strength.
Would you please help putting this desperate man into sleep? I want to save him from his curse.

Thanks in advance

[Aerich]

It's a tough fight, for sure.

Tactical Spoilers
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If you can manage it, try and separate your party a bit so they all don't get hit by the same spells.

I've always attacked the warriors first, then mages, clerics, archers, and finally the luremaster. It's exceedingly important to use one or more characters/methods to disrupt the spellcasters while you take out the warriors.

I beat the fight last time by the following:
Summons to help keep spellcasters occupied and one elemental to take pressure off my fighters. Use of Melf's Acid Arrow and an archer to disrupt the mage(s), with an occasional spell to help the fighters. Other characters focused on hammering down the Luremaster's warriors. As the warriors go down, switch to the mage and the cleric, and replace the now-dead summons with more summons, this time near where the additional archers and mages spawn. If your fighters take too much damage, either get them healed or pull them back and switch to missile weapons.

I last beat the Luremaster on Insane difficulty with a paladin, mc ranger/cleric, mc fighter/druid, dc fighter[13]/mage, mc fighter/thief, and a bard.

The bard and the fighter/thief spent the majority of the fight right where they appeared, providing the necessary disruption among the enemy casters. The bard didn't use songs, as he was much more valuable as a spellcaster. Because the heroes hit so hard, War Chant is a drop in the HP bucket. The fighter/druid cast the first set of summons and engaged the cleric. The fighter/mage, paladin, and ranger/cleric took down the warrior heroes. The f/m had to withdraw after the warrior heroes were dead, and cast spells and used the returning throwing axe for the remainder of the fight. Paladin and R/C healed themselves and charged off against the cleric and first mage, while the F/T sneak attacked the second mage that had just spawned. The bard summoned an elemental to attack the archer off to the left. With the cleric and first mage dead, I focus-attacked the last mage, then the remaining archer, who had just finished off the elemental.

The Luremaster was last.

Took me three attempts.

Key spells: mirror image, stoneskin, slow, haste, recitation, Shield of Lathander, elemental summons, magic missile, Melf's Acid Arrow, flame arrow, heal

You could also try symbol of hopelessness. For best results, use a recitation first.

[enrirex]

I made it. But in a different way. With this strategy, he is real simple, really

First of all, I cast every protective spell that I can (plus Haste). Enter in the portal. Then, I just cast Chromatic Orb with my bard to paralize him, charge with EVERY member and bring him to death, while ignoring the other villians.

Poor strategy, but super effective