On the litter box training, just keep trying. 4 weeks is a little young for some kittens, but eventually she will see the others using it, and pick up on it herself. On the girls nursing on the little male, it’s fairly common for kittens to nurse on each other. Not something that you want to happen though, so separating is about the only thing that is going to work I’m afraid. Try putting a ticking clock in with his stuffie, maybe the sound will help him. Poor little guy.