Think the kill order in this video is good. Just need someone to interrupt the Warshaman. The adds doing the whirlwind can be taunted by the tanks - the extra dmg is just healed through.
For Ath, the sniper isn't *that* dangerous if you just focus yourself. The problem can be camera angle cus you'll have your back against a wall most likely, so while healing yourself through sniper dmg, you might miss an aftershock (the fire lines). Also, track Bonecracker and Magistrike on your frames. Magistrike can be dispelled.