So sorry that it's been difficult for you. However, I don't think it makes a difference if it's the mum or MiL who makes problems, for bride or groom, I think it's all down to personalities!
One of my darling stepdaughters got married, I have been her stepmother for many years, and I was delighted to be one of their two witnesses along with a friend of the groom.
We all agreed approx what colours, more or less to wear, including the bridegrooms mum and family.
The wedding went well and I don't know of any problems BUT nevertheless the bridegrooms mum has made it VERY, VERY clear that she is the proper 'MUM' and 'NANA' for the happy couple and their baby, and she is VERY controlling in many, many aspects of their and their baby sons life.
I have kept my mouth shut (except to my friends!) and thankfully all seems well but I do at times feel I'm doing a difficult balancing act re the MiL. It would be VERY interesting to know what she really thinks of me and why she gives the impression that I'm an incapable twit!
Hope it all goes well for you, please don't get upset at anything, and we all hope that the happy couple have a wonderful day and a perfect start to their marriage - we are the participants, not the main players, in their marriage and their life. ?
PS I have found so many of these posts helpful for me personally - at times I do feel completely excluded by the MiL and its great to see how other gransnetters cope with the difficult 'other'. I get on with my life and enjoy my work, family and friends and doing what I can, when asked, for my stepdaughter and her family. ?