2 Heal it. We have 2 hybrids (Ele sham, Shadow priest) and two MS healers (Disc preist, Monk)
When two MS healers can't go down, we send a hybrid that doesn't have voodoo or debuff. Never send the Hybrids together down at the same time. Then its GG. Just don't over think it, only when your healers can't go down, send one of the hybrids.