Something along the lines of...

Mage "slave"
/tar [target=focus, nodead] focus
/stopmacro [target=focus, exists, nodead]
/assist Toon
/focus

With Main Tank
-Same Keybind- Mark that mages target with Raid Mark such as Moon...




And then another for that mage.
/cast [target=focus] Polymorph



The first macro will (on your party leader main) mark the mob as a CC target.
On your mage:
- Target your focus if you have a focus; or
- Assist your main and make that target your focus.

When setting macro's have a /clearfocus button for all toons... then...
On the main tank, you press the CC acquire button for slave 1, which marks it.
Choose next target and press the CC acquire button for slave 2 etc...

Once the CC's are chosen, each has a button to CC its focus target.
I'd give each their own CC button to activate the CC, but you could have them on the same keybind if you wanted.

For my mixed PvE team, instancing as the goal...
Numpad 1: Mage set focus / Numpad 4: Mage Poly Focus
Numpad 2: Warlock set focus / Numpad 5: Warlock Banish Focus
Numpad 3: Priest set focus / Numpad 6: Priest Shackle Focus.

Pretty easy for me.. 1/2/3 for setting focus, the key above for CCing the focus.
Everyone will have their own system. This one works for me, maybe you can adapt it for you.