The clones phases are the most healing intensive of the fight, especially the first set where everyone is crammed into a small area and getting hit by Garuda's Friction aswell.
Whoever is off-tanking should just focus on one of the sisters and try and keep hate on it while DPS burn down the other one. You or the other healer will be tanking it but it doesn't hit all that hard and you should just be able to heal through his attacks with no issues.
