the best way to off tank the sisters imo is to have the healers/mages not burn any CD, cause the moment a whm does heals it will instantly go to that person. The off tank must pull the red and aim it towards the plumes and away from the party. Cause a cleaver can instantly wipe the party clean. While they handle green and kill it asap because yes it can heal garuda. If your party's dps isn't sufficient this fight can be bothersome, cause it will repeat that same phase over and over and over till you can kill it. But the role of the off tank is to grab hate asap and if you can't handle that, that fight will be a problem. I've done about maybe 30-40runs with this with my fc, to the point we just kill it before it even reaches the 3rd sisters.