Honestly I think both kittens would be happier as only cats, so if you can bring yourself to part with bully boy , do so.
Otherwise, go on feeding them apart for a while, and when you try feeding them together, growl or hiss like a cat at your little bully, when he tries to bully his brother.
BUT make time to play and cuddle with your little bully alone - simply shut his brother in somewhere else, so bully boy knows you love him too. Don't let him claw or bite you, cats can learn to understand the word NO spoken calmly every time they do something wrong. Taking him by the scruff of his neck and shaking him gently is what any grown cat would do to him, if he or she was gentle, otherwise they would slap him soundly across the face so the summersaults across the floor, which I don't advise you to do.