For fuck sake, use your brain.

You have four characters going in diffrent direction, One button is pressed, how do you think its done? One button, is bound to a diffrent movement direction on each character.

E.G Character one the = key is move forward
Character two, the same key is move backward
Character three, the same key is strafe left
Character four, the same key is strafe right.

I don't understand why you want to use a formation, it only makes things look slightly better, it has very little impact on gameplay. Get the other aspects of your setup nailed before you start trying to make it look "pretty" and put the finishing touches to it.