If you use IS Boxer, just about every vehicle will automatically follow the active toon.
Just get everyone mounted, and press your follow hotkey.
Or switch from one active toon, to a different active toon, if you have automatic follow on a character switch.

So far, the only one which has not auto followed (and "/Focus ToonName" -plus- "/Follow Focus" also failed here), is the quest where you become the giant in Zul'Drak, and need to kill 100 scourge plus the three named guys. Have done all the quests with vehicles through Borean Tundra, Howling Fjord, Dragonblight and Grizzly Hills (most of the vehicle quests were dailies).

For every vehicle which follow works fine with, the vehicle attacks broadcast just by pressing their numbers, generally 1 through 6. And as always, the slaves automatically assist the current active character, just by pressing the attack keys.