Here is the 'w' script for my dual box, just add more id clones for more. '-' is a macro set to follow my main.

[code:1]#IfWinActive, World of Warcraft
; *** Makes wow2 follow Wow1 Player ***
~w::
ControlSend,,{- down}{- up}, ahk_id %idClone%
return

#IfWinActive, World of Warcraft
; *** Makes wow2 stop following Wow1 Player ***
~w Up::
ControlSend,,{w down}{w up}, ahk_id %idClone%
return[/code:1]

My only concern is that the follow macro is spammed while the button is held down (when you are moving) although this has yet to actually be a problem.