The only movement that can be automated is /follow, which cannot be modified. You're stuck with clever positioning/movement of the main as your sole control. Also note that not only do you need the others in range, you need them BEHIND the target if you don't completely overpower it so you don't give it a slew of extra attacks off your collective misses, hosing your main. This is why multiple-melee multiboxing is not recommended.

It can be done, but the problems you're talking about...there's no way to get rid of them, you will always have to just deal with it.