First boss is easy, all he does is spam shadow bolts. Use fire eles to get rid of the mobs that spawn every 20 seconds (and/or thunderstorm). maybe start off with only attacking with one shammy to make sure he gets aggro and keeps it. then just go lightning bolt, lightning bolt til death.

Second boss, pop heroism and earth eles, nuke the cast (start with groundings down and continue to refresh them) then switch to the melee dude. Hopefully the earth eles live long enough. Chain heal if needed, don;t forget groundings.

For last boss, he hits hard, one of your shammies will have to be tank. First phase, is lightnign bolt, lightniong bolt heal. Stop all casting during the roar. Avoid the aoe cone attack, the boss doesnt move/turn during it. After he dies, he resses. And gets a lot worse. Stack your gifts of naruu (i ur ally), pop heroism, and fire else. nuke down fast. If he roars, stop casting. Avoid the aoe cone again. If things slow down, do heal selves, heal tank, lightning bolt, heal selves, heal tank, lightning bolt. Thunderstorm every time it's up for mana.

I run 4 shammies.