I like tanking the Emps with my back against the wall right below the stairs where you enter the room. There is less bugs than directly under the torch. Normally I can Demoshout all fight long without worrying about bugs at all. Make sure you coordinate that with your healers before the pull.
But really maybe you should have dug up an old threat about the twins instead of asking in this one.
I remember first being amazed when two identically geared and specced tanks tanks Twin Emps, one using Demo on Vek'nilash whenever possible, and the other not, and the latter was taking easily 25% more damage total.
Late comer to this thread, hope you'll tolerate this small derailment. Is there a trick to using Demo Shout on the Emperor without aggro'ing the neutral bugs around?
I can keep it up reliably just by going where the bugs aren't - if there's one bug on one side of nilash, move to his other side and shout. just get a good feel for the range of demo shout and stand against the wall when you have to, it's not like standing on top of the tank is going hurt you and there are no bugs behind the wall
at this point, though, I don't bother and just DPS since our tanks are geared enough that the extra melee damage is a non issue