My daughter has been in a similar situation. My son in law's family ruined their wedding. They said they weren't included in the wedding preparations (I tried my best to include them in it all, reminding my daughter and son in law not to forget to include his mum). It was only a small wedding but none of them spoke to my family at the reception and we didn't have a clue why. Apart from the fact that they felt excluded, they had listened to gossip and tittle-tattle about our daughter and had decided that she wasn't suitable for their son. (We get on very well with our son in law). SIL's parents stopped speaking to SIL and my daughter after the wedding. They went round to find out why and there was a big row, with SIL's mum having a real 'go' at my DD.
DD stood up for herself and all sorts went on. My DD and SIL now have a daughter of their own, who is lovely and well cared for. My daughter's mother in law has long since apologised to her, saying that she was wrong about her and telling her that her daughter is a credit to her and they now get on very well. My daughter has helped them in lots of ways and they realise they were wrong. I hope the situation improves poppyfields.