Use a bunch of summons to keep them off your weak characters. You can set the room up as you please before sending an unwitting summons to die. Remember where they spawn and hide in shadows or go invisible at that spot and wait for them. Buff. Negative Plane Protection. Get more summons spells/wands/items ready for use mid-battle.
And, C.F. stunned them quite well for me.
And, as a thought, though I've not tried it, DAYSTAR.
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