1) Write
this setdammage 1
in the init field of the unit. They take a second or two to die ;D so make sure the player is looking the other way.
2) ditto
3) check out the sound tutorials in the Ed Depot
4) Create a trigger over the relevant area:-
activation box: West present (or whatever)
type: switch
Create a set of waypoints for the East group. If it was a patrol they might go
MOVE
MOVE
MOVE
CYCLE
SEEK & DESTROY
In other words you want them to cycle round the patrol route until West is detected and then go to a certain area for S+D.
Now Synchro (F5, drag and drop a blue line) the trigger to the Cycle waypoint.
Hope that helps