The big question is: do you use focus to set up your main, follow, and assisting?
If you do, then alternative targeting can come from [mouseover] macros or a manual target selection. i.e. i hit mouse 4, and all my toons target the mob i'm going to kill. Then, while fighting, i target somethign else, and hit another key that has a lock /assist my target and send their pet after it. This would be pretty cumbersome.

If you do not use focus for setting up which toon to follow and assist, you can target something before your fight, set it up as one of your alt's focus, and evertime it needs CC, i.e. secubus seduction, you hit a macro that says '/target focus /seduce /targetlastarget

You can probably search these threads for 'focus' and find alot more on this topic.