I haven't thought this through, but I want to try to help. I LOVE focus. What if you focus your main. Have your alts get a target if they don't have one (and never change it), and just assist the focus.

So on mages:
/target [target=target, noexists] focus-target (I want it to only target focus-target if it doesn't have one, but do nothing if you already have a target)
(now they have the mob they will sheep)
/cast [target=focus-target] SpellofMagic (they still have sheep mob targeted, but they cast on focus' target)


That might let you target a mob for CC and still DPS. (if it works)