It seems to work quite nicely. The first enemy opens the first door. They all have the same variable at 0 however. How did you connect the first enemy with the first door exactly?
They all start with variable at 0 so on the:
On start of Layout | set InstVar to Self.IID
it replaces the variable with each object's respective INSTANCE ID. You could start there or manually assign the variables.
I like using that since it takes less work. Now it's just a matter of repositioning the enemy sprites. You can even modify the capx so instead of destroying the enemy it simply toggles a variable to open/close doors...