You have:
- FTL Target Me
- FTL Assist Me
- FTL Follow Me

You could build it into the same macro.
One step.
- FTL Assist Me
- Send Keybind to Slot/Character for CC Macro.

You can do it in two mapped keys or two steps on one mapped key.
Key A, or Step 1.
- FTL Assist Me
Key B, or Step 2.
- Send Keybind to run the CC Macro.
If you went this route, it could execute a step on press or release.
And the delay between acquiring target and setting the target as the focus, would account for latency.

You could have all your mages in an Action Target Group.
Instead of Send Keybind to Slot/Character, use the ATG as the target.
And round-robin within target group.

There isn't something for your slaves to focus the target of the current window.
But you can have your slaves target what you're targeting now.
And once you have assisted, set that as your focus.