I clear heroics with 5 shamans and did so before I had the gear I have now, earth elementals and a crazy amount of patience are your friend. The fight I have the absolute most trouble with is the vael fight in BWL, I just don't think it's 5 boxable you need more victims

A good tip for trying to box without a tank is seriously don't worry about aggro and have a nice solid spam button for heals on your healer. Spam it constantly forget mana it's an attrition battle. I also pop bloodlust very early in the fight if not just prior to the initial pull, getting all the DPS you can out of each toon is important, and it does no good to pop BL or trinkets right as one of them dies.