If you use IS Boxer, vehicles will auto assist the same as toons.
Press 1, and everyone presses 1, at the lead toons target.
The same naturally for 2, 3, 4, 5, etc.

Not all vehicles will follow the other vehicles.
But most will, just get in and do your normal follow key.

If that doesn't work.
Clear focus, then /Focus ToonName, then /Follow Focus.
This will work for just about anything.
But again, there are exceptions, in which case you either manually control each and do the quest or skip that content.