Assuming it is with the first team mentioned in your signature:

- do you use lay on hands when your tank is almost dead?
- you can assist your priest with your shaman in the healing from time to time: if key 1 is your dps key on 3 toons, then copy it to key 2, but for the ele shammy add a target tank chainheal in the rotation. Just use key 1 to dps, but when your priest can't keep up switch to key 2. Your 2 dp's will keep dps'ing but your tank will get extra heals.

Back with my crap gear i used to spread my toons out as far as possible from eachother. Engage in the middle and tank as far away as possible, making sure you face him away from your team.