The simple answer is I doubt you'll be able to do what you want.

What I found was that you cannot have a slave /follow a toon that's already within a vehicle. I have the slaves get in their vehicles and /follow the master, then he gets in. If they break follow, the only way to re-follow is to have the master get out.

Note, many vehicle actions, such as jousting, will break follow and thus force you to go through the above pita to re-follow. For ToC jousting, I'd just place the non-active toons to the side and have them assist and shoot the shield-breaker shots while i pound down the target on the active toon. For ToC instance, you're sol.