here is what i'd do:
Demonstalker:
#showtooltip
/cast [mod:alt, target=player] [mod:shift, target=demonslave] [mod:ctrl, target=demonservant] [nomod, target=player] Rejuvenation
Demonslave:
#showtooltip
/cast [mod:alt, target=demonstalker] [mod:shift, target=player] [mod:ctrl, target=demonservant] [nomod, target=player] Rejuvenation
Demonservant:
#showtooltip
/cast [mod:alt, target=demonstalker] [mod:shift, target=demonslave] [mod:ctrl, target=player] [nomod, target=player] Rejuvenation
ALT - casts 3 rejuvs on Demonstalker
SHIFT - casts 3 rejuvs on demonslave
CTRL - casts 3 rejuvs on demonservant
Pressing it without any mods will make each one target themselves and cast rejuv on themselves.
note, this macro will probably not work if you want to rejuv someone outside the party, unless you have an option before all of the criterias above to Rejuv on mouseover. just add [target=mouseover] after "/cast" and you should be fine. might be buggy though with three druids. might just wanna use mouseover on main.
