Ultimately, you have two very general options.

In option A, your slaves assist your main and cast a heal at the target of the main.
In option B, all of your toons cast a heal according to the macro you have created.

In option A:
You have one heal macro which is good for all of your toons or any friendly target.
The main targets something, and the slaves assist the main and then cast the heal as the main does too.

In option B:
You have one heal macro per potential recipient of a heal.
Clicking the Heal Toon 1 macro has all toons healing Toon 1 at once.
You don't need to get the leader's target and assist him/her, but you do need a macro per heal target.

I personally like option A, with macro's like this:
#show Lightning Bolt
/cast [help] Lesser Healing Wave; [harm] Lightning Bolt