Here is the code I am using, the initial value for Health is 4 so in theory the final value after destroying all the EnemyTurret_01 should be 0. However, this does not occur when 2 are destroyed at the same time.
Seems you could do this: add 'for each' loop after health <= 0, OR add 'on destroyed EnemyTurret' trigger where you move the 'pick instance..' - part.
Also, it seems like your creation method could benefit from containers, or a for loop. You can use loopIndex to pin them to proper imagepoints: Spawn EnemyTurret_01 (image point "Turret_000"&loopIndex) :)