Insurance and CO

CO says that DH and BM will split uncovered medical and dental expenses. They both cover their daughter under their dental insurance plans. I also cover my SD under my dental plan. She just got braces, and my insurance ended up paying more than we had expected, so I received a small refund. Am I legally obligated to split it with BM? Or do I get to keep it because it was from MY insurance and I’m not a parent and therefore covered by the CO?