I have no end of trouble with this bit every time I get to it.
You can use any summoning spell/wand at all, just get a barrier between you and the mind flayers. Undead work best, because they don't have brains, but as you don't have that, your main aim should be to stop them getting near you. Any wall of flesh will help!
It's true that having a party who's total intelligence points you can count on one hand doesn't help.
Also, try setting the game difficulty to the easiest setting for the duration of that part if you are really stuck. You can always put it back up again afterwards. I know this is cheating, but it is annoying to start again after getting that far!
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Time is an illusion. Lunchtime doubly so.
Epona of The Laughing Hyenas.