If you use a Focus based assist system.
A basic part of that is having master switch keys.

Everyone has one key per the number of toons on the team.
In this case there are two characters, so everyone has two leader switch macros.

Both of them focus the first toon, on keybind A.
And both of them focus the second toon, on keybind B.

Both of them have:
/cast [@focustarget] Whatever
/castsequence [@focusttarget] Whatever, Whatever, Whatever

Both of them have:
/follow [target=focus]

Etc...

No matter which toon leads... that toon is everyone's focus.
Set their warcraft focus macro keybind, to whatever key your software uses to switch between their windows.
So the focus auto changes, when you switch screens.