I have an ex that was inactive in my child's life until his current wife forced him to start overinvolving himself, wanting for her new family to be whole.
As a custodial parent, the more you push this issue with a half active father, the more the kids are going to pay the price. If he, as the father doesn't want to enforce his rights and she as the custodial parent doesn't want to give up the additional rights that she has had, why not focus on the family you do have, you, your husband and your children.
You are trying for a battle that no one wants to be in, if you feel so strongly that he needs to be a more active parent then he is, you need to make the choice about your relationship and what you can handle.
Weigh out the good/bad here and figure out the importance of pushing this battle on all parties or just accepting the situation you have. There isn't anything that requires you and the ex to be friends. If the situation was working for your husband previously, he has to be the one to determine that it is not working now.