Here are the four macros four each shaman respectively:
You can continue to cycle through targets by spamming while chain heal is being cast.

/targetfriend
/cast Chain Heal

/targetfriend
/targetfriend
/cast Chain Heal

/targetfriend
/targetfriend
/targetfriend
/cast Chain Heal


/targetfriend
/targetfriend
/targetfriend
/targetfriend
/cast Chain Heal