Also, why would one ever cast a healing spell (Force Lift) on an enemy?
Force Lift is a mez and more importantly an opener. Forget the heal, it takes an opponent out of the fight for a minute. Force Lift is one of the Sage's most potent abilities. It should not be ignored.
For my healers, personally, I would respec to Balance for this quest and leave the healing to Tharan. But if you stay in heal spec, you should do as others have stated. Mez the strongest enemy, focus fire on the remaining. Be ready to run if necessary.