Male cat has been coming to my house, is he not neutered?

It's familiar territory. The cat recognizes the scents and is coming back because it's comfortable. You shouldn't let him in your house at all, he probably wouldn't take to well to a new cat on his old territory. I know you can't get your dad to spay your cat, but keep trying. It's very important as female cats have ways of slipping out of the house when they're in heat. And please (just to be clear) no matter what age she is and whether or not you can take care of the kits, don't breed your cat. Also, talk to your neighbour about keeping his cat indoor if you or your dad are uncomfortable about him being outside. Hope I helped!