[AS2; Flash 8] Space Invaders Style Game - The Aliens

I am working on a Space Invaders style game, where the aliens (in formation) move left and right. Every time they hit one side or the other they drop down about half their height. (I’ll just call it a step). So they move down a step and then repeat till they “land”. So my problem is that whenever they hit a side not all of the aliens reverse direction as soon as they hit.

My work is here for your reference.