For IS Boxer...

Put the toons that you will want to receive mouse clicks (broadcast the mouse) into an Action Target Group.
Open the toolkit, and towards the bottom of the top pane is action target groups.
Left click that, then in the lower left pane create an action target group.
Rename it to something that had meaning for you.

I personally have spells which mouse broadcast on three keybinds.
Depending on the team.
Not everyone on the same team will have a mouse broadcast spell on the same keybind.

For example on my 4x DK + 1x Paladin team, Death & Decay is mouse broadcast while the Paladin does not have a broadcast spell.

Anyway, to avoid conflicts I have an ATG for each of the keybinds I use for mouse broadcasting.
And then add toons to that ATG.

Then I set up the hotkey for a Send Next Click action.
Not all toons will AoE on DPS 4.
But for those who will.
Expand FTL DPS Keys, by selecting it in the top pane.
Open it in the bottom left pane.
Select DPS 4.
Expand it (bottom left pane).
Click the 1 under Steps.
Then in the bottom right pane, right click on Actions.
New Send Next Click Action > Target: The ATG for DPS 4.
And Block Click from the Current window should be checked; that way, everyone in the ATG receives it by virtue of being in the target group, but no one not in the group gets the click even if they're the active window moving the mouse and clicking.

Remember to Export to Inner Space (in the File Menu).

In play...
I press "4".
Which does all the normal stuff on "4".
IE:
- Slaves assist the master.
- All windows receive a "4" press... which casts whatever is on "4" in warcraft.
- Anyone in the Action Target Group (AoE_On_4) also gets a mouse action.
You move the mouse on the current window and will see a copy mouse move on their window too, if it is a ground target spell like Hurricane or Blizzard or Death & Decay, you'll see the targeting circle move in the slave windows as you move the mouse in the main window.
Once you click in the main window, that click is broadcast to all the slaves who are receiving Send Next Click, at which point the mouse broadcasting is automatically disabled for those characters.