Something similar happened between my matron of honor and bridesmaid. It's been over five years and the matron of honor is still annoyed that the other person didn't pay half. And the bridesmaid was upset that the other person spent so much more than she could afford. And here's me in the middle (representing your child), wishing that these people were smart enough to work things out in advance.
You and/or your husband should have spoken up before accepting money from them. More to the point, even if someone says, "money's no object," an upper limit should be agreed upon. Since that didn't happen and you've accepted the money, I think you should learn from this and then let it go.