[Pirengle]

*sigh* Most of these suggestions won't help you current situation, Jinny. (C'mon folks, 7th level spells? Artifact weapons? Those require beating Chapter 5, and I'm guessing this problem is in Chapter 3.)

The mind flayers fire off an undispellable stun, and if a character gets stunned, the flayers will crowd around the stunned person and suck their brains out. If their INT score hits 0, they die. Beating the mind flayers requires protection from the stun and the intelligence drain.

If you have a cleric that can cast Chaotic Commands (5th level spell), do so. Or hit up Roger the Fence for all 3 of his potions of clarity. They do the same thing, but their duration is a lot shorter. Those will protect against the stun. Also pick up Roger's potions of Genius to counter the mind flayer intelligence drain.

Take all the characters with Chaotic Commands/Clarity potions and keep them near the doors. When you open the doors, the umber hulks should come charging at those characters. Take the rest of your party, equip them with missile weapons, take aim at the mind flayers behind the umber hulks, and fire. This might take a while, but it's a bit easier for a young party.

Bloodtitan's suggestion won't work if you've installed the Baldurdash patch. (I suggest you download and install the official patch from Interplay.com and the Baldurdash fixpack from Baldurdash.org)

You can also wait until Chapter 6 to solve this quest.