You have some way to broadcast keys.

So your pally can spam their 96969 macro.
Your priest can heal the team as needed.
And your dps can do their pew-pew-pew.

If you're using something like Keyclone, have keys on a blacklist which are not passed to the slaves.
But then unbind other keys on the main (in warcraft) so you can move the slaves without moving the main.

If you're using InnerSpace, have repeater off (default), and don't bind WASDQE to any Keymaps.
So pressing these don't broadcast, because they're not in a Keymap.
Then make keymaps for the Arrow Keys, which broadcast to all windows without the current.
That does the same (entirely within the software instead of software + wow), where you can move the active toon or the slaves without moving the other.

Hardware boxing would be similar to Keyclone.
Have keys which are bound to the clients on the other systems, but not to the main.
So you can press down arrow, which does something when broadcast to other systems.
But does nothing on some systems.