Trapping cats is actually pretty easy. You get a long cage at a tractor supply store, hardware store, or hunting store. Buy one can of cat food, smash up in back behind the pressure mechanism for the door so the cat must step on the mechanism to eat the food. Cover the cage with a blanket and wait. Along a wall where the cat has been seen is a good location to leave it. You will catch them.
You can either release them somewhere else or soak them with a hose and release them. Chances are they will not come back after you blast them with a hose. Your local municipality may also pick them up for the pound - depends on the local gov. Also be aware that they will go ballistic if you take the blanket off because cats can't deal with being trapped. So if you are an animal lover, handle with care...