Posted this in my heroic summary post. Don't tank, spread out to avoid aoe damage, dps zerg medic->chief->commander. Most of the damage in the fight is random anyways, so just need a good healer.
We did it another way, we had out tank pull the Melee boss to the stairs where you enter.
Tank was the only one in range of Main Boss' grenade spams, killed Melee -> Main Boss -> Medic.