Pretty much what the topic says. CC doesn't work on these guys at all.
Is that intended? I can see maybe on Hard mode but on normal it really becomes trial and error and a lot of luck to get past this encounter. Ran it twice and both runs had multiple wipes on this boss.
We did this with 2 level 27s (Sorc, Jug), a level 25 (Marauder) and a level 21 Mercenary Healer.... It was pretty rough... we wiped once...
here's what we did and it worked 'fairly' well...
Tank took both DPS characters (The gunner and the dual wielder), the maurader in our group took the other 2 mobs. we kept damage pretty even on all 4 throughout because each one you kill makes the others stronger so try to 'kill them' all at once.
the dual wielder chick kept kiting over to our sith sorc so the tank had to keep leaping over there and taunting. That mob bounces aggro all over... the trick is just using stuns, knock backs etc on her and then taunt her (which keeps her aggro for about 10 seconds). The gunner (dps mob) shoots at the tank as he chases the dual wielder but he stays positions for AE's.
I hope this helps you succeed in the future.