It's so hard when they are *blinded* by love. My Dad is the same. He thinks that his entire family is just being spiteful by not liking his wife.

Anyway, Carley has a great suggestion - make it very clear to them that it would hurt you immensely if they carried on with rot on your babys big day. From the sound of it though the only problem would be with his wife and not your exSM. Besides, she has become a close friend of yours now, so it shouldn't matter what the familial relationship used to be.