that's not how it's done.
even if you could pass the mouse, each character has a different location and a different point-of-view. as such, even if you could click-n-hold to drive, they wouldn't go in the same direction

using the keyboard will coordinate your actions and using /follow will keep them together. couple that with some creative wow keybindings for formations, and it'll work as you expect

mouse < keyboard for multiboxers