What? No, I meant call the new script (setUnitPos auto) from the deactivation field of the original trigger. You need only one trigger, which should be attached to the group: the easiest way is just to setpos it to the position of the group leader. Actually you don't need scripts, just put the relevant code in the Activation and Deactivation fields.
Communication between triggers is carried out by global variables. You can use them to turn other triggers on or off when a trigger is fired/deactivated. The name of a trigger is just that, the name. You need to use the name as a paramenter of a command before anything will happen.
I suspect the distance you are trying to measure is the shortest distance between any east and any west in the area. This is messy, as you have to create an array of each and then find the distance between every pair ... then pluck out the shortest one. By which time they've probably shot each other and you have to do it again. You'll also risk rapid switching between one script and the other as the front enemy is detected (on), killed (off), the next guy moves up (on), he is killed (off) and so on.
Have you thoroughly tested OFP procedures in the kind of circumstances you are considering? They may be better than you think .... they often are.