Problem is i want to stop these all duplicate instances on their same Axis if any one of them reach in the middle of screen but it is not working it overlap each other till they don't reach in the middle of screen.
Could you clarify what you mean by them overlapping each other until they don't reach the middle? I'm not clear on what is happening. If you could upload your .capx file it would really help.
Also, how are you detecting when they've reached the middle of the screen? If you're doing it by collision with another object, you may need to add a "pick all" event to pick all the other bullet sprites. Otherwise your action will only affect the one sprite instance that did the colliding.
I made an example here but I'm not sure if it's doing what you want from your description.http://storage.wertle.com/construct2/bulletThing.capx