Tallullu has given you a great link! regarding bonding.
I just wanted to add a safety tip: Be sure the cats nails are always trimmed. Even during play, when I cat is not trying to harm a rabbit, it can scratch a bunny. I've heard of bunny's eyes being scratched and even if it's just a skin wound, rabbits have a tendency to develop abscesses from cuts, bites and scratches.
Also, your bunny is reaching sexual maturity at 4 months and may try to get fresh with the cats, even females will hump to show dominance, which in turn could cause the cats to get agitated, aggressive or scared - which in turn could cause them to lash out with their paws.
Also be careful that the cats can't reach in with their paws into the bunny pen/cage.