So is there any other way I could make my enemy detect if the player is near it?
Why would someone want all the sprites in the container destroyed if one is destroyed?
Containers, in essence, are used for making one whole object out of several pieces. It's for ease of use when making compound objects. Rays, bullets, and other temporary things that a sprite creates should not be a part of the container.
If your sprite is spawning sight detectors, they're going to be destroyed. If the detectors are in the same container as your sprite, your sprite will be destroyed also. So the best thing to do would be to not put your sight detectors in the container.
If you're having trouble linking a sight detector with it's originating sprite, then put some kind of identifying number into a private variable when the detector is created so that you can keep track of it.
I don't know about your button though, for some reason your cap won't run for me.