its actualy not that hard, heres my heal setup...

1 - heal Mt - druid only castsequence
2 - Heal Ot - shaman only cast sequence
3 - Heal target - all 3
4 - group heal group1 - priest + sham
5 - group heal group2 - priest + sham
6 pbaoe insta heals (CL self on shammy)

I dont use each healer to there full potential but its actualy got some benefits to seperate players, the fact u are managing all 3 mana bars means you use abilities when the group needs and not just yourself giving priest innerevate, using mana tide totem etc.