[Radek]

I haven't any problems with mind flayers. Well, a bit of cheese is involved:
1. You can pickpocket Mordekainen Swords and get Greystone Amulets. These greystone amulets are special: they have only one charge but they are already active and their activity do not wear off! DO NOT activate the amulets at this moment! Equip them - that's all.
2. You can sell the amulets (yes, they aren't "stolen") and buy them back. Now, you have Greystone Amulets with 30 charges, which are still aready active and which do not wear off. The "no wear off" property is valid only for the special, already active, charge. If your protection is dispelled (beholders, for example) then you still have 30 short time protections (you have to activate the amulet now).
3. The Greystone amulets give you almost complete protection from mind flayers. They do not protect you from INT draining but they protect you from stunning, paralyzing, and mind control of all kind. Mind Flayers are unable to dispel your protection.
Therefore: cast Mordekainen Sword and pickpocket it repeatedly until you have 2 amulets for each of your guys. Sell the amulets and buy them back. Use one amulet when dispeling do not threat - the special charge gives you unlimited protection. Use the second amulet if mages or beholders are nearby - the special charge gets dispeled but you have enough short time protections still.
Now, mind flayers should begin to tremble. Equip the amulets and take mind flayers one by one. Note, you are protected from the always present umber hulks, too.