Gang-rape Bloodboil to death. Then get the others to 40%; kill Jubei'thos first, then Dia. Don't push Dia under 30% until the other is dead.
-Tank Dia away from the other bosses. When she transforms, big heals on her tank.
-Avoid the big flying ghosts when she fills the room with shadows.
-Mark of the Necromancer: the shit ability for this fight. Do not dispell it unless you are Hallaer. Take it to the edge of the room when she casts Reap.
-Kill the Jubei'thos' mirror images.
-Avoid his boomerang (move away from the arrow that points out of the boss)
-Spam heal and BoP Bloodboil's fixated target. Move away from tank to allow tank debuff to drop.
-Move out of Leap damage zones (Blackhand's Demolish)
We're going to use two disc priests to help off-set the health debuff.