Why go through all that trouble of casting a blade barrier? You'd have to sleep quite often, wouldn't you? And don't they have MR?
Personally, My Archer Legolas does all the work on the mindflayers. With his trusty bow and arrow, boots of speed, ring of free action and whatever item works against domination they don't stand a chance.
Here's how it works:
Lock your entire party safe for the archer in a room so they won't be seen. Then hide the archer.
Find the flayers and start shooting at them. When they notice you, retreat while firing more arrows at them (or the umberhulks, whichever are nearer). Go round a corner or out of sight and hide in shadows if you can't retreat any further. Then run to the other side and repeat the tactic untill they are all dead. If one manages to land a blow for whatever reason, you can hide until you recover
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The last arrow of Legolas kindled in the air as it flew,
and plunged burning into the heart of a great wolf-chieftain.
All the others fled. -J.R.R. Tolkien, The Lord of the Rings