Your instances were getting confused because you weren't specifying which gun sprites belonged to which laser sprites.
I added a couple of For Each loops and a PV called 'gun' to keep track of which laser sprites belong to which gun.
The guns are labeled 1 and 2 (check their properties), and when they spawn a laser the laser gets tagged with the same number. That way when you tell the laser parts to line up their .Y location with a gun later on, they know which gun to line up with.http://www.box.net/shared/hv4a8jp4iv
It works fine now.