Eteocles is correct... there is no proper way to have the mouse replicated on the same machine, without bouncing the screens all over the place (due to focus jumping in order to allow the screen to process the mouse message)

and drag events definitely won't work.

and if your goal is to keep them sync'd so you can drive around using only the mouse... that won't work.

you will need to utilize /follow to get your alts to follow.

personally, for the long hauls... i use /follow to get the alts in line, then numlock for auto-run ... and right-click/drag to steer once in a while. once in an area, i occasionally will spread out my group into a formation... spin and/or strafe.. via the keyboard.

best to get use to it early