If you have sincerely attempted to appeal to those family members who are at the core of this constant discomfort, you've done your best. I suggest that you and your husband write letters to your families, asking them to participate together in family get-togethers and celebrations. These letters shouldn't be an attempt to lay blame on any family members, but should appeal to them to be the involved, loving family that you want and need in your lives. Follow up those letters with heartfelt discussion. Be sure to ask them what they need from you so that these family events can be an enjoyable time for all involved.
If getting both families together casts a pall over what should be a joyful event and turns into into an uncomfortable affair, let both sides know that you are not going to continue to expose your daughter or yourselves to this unnecessary conflict and tension.