Crikey Diana! It's obviously an exercise in control by his family, as you have rightly guessed. Some people really misinterpret NO and think it's some sort of mind game.
I'm useless with any new advice, actually with any advice. I did not have this thing to deal with, both because we culturally don't have them and because at the time I lived far from the place where we got marred, so it would have been a logistical nightmare anyway. But we had our fair share of "why?! what?! no, you're not going tos...", etc to deal with. But, we were determined to make it a day for us, not a day for others.
For me, living abroad and getting married back home meant I had to organize everything remotely, with just one trip to book the date at the registry office, check the venue, book the musicians and talk dress design with the seamstress. That turned out to be the blessing! With nobody to stand over my shoulder and suggest all sort of things, from customs and traditions I hate, to finer details, we could actually do everything in a very relaxed manner. Everyone just had to turn up and see how the day would unfold. It was lovely, very 'us', simple, about things we wanted to share. I think everyone figured early on things were going to be just a bit different than 'normal', so they weren't anticipating anything, just watching and participating if they wanted. No unfulfilled expectations. We had one rule - nobody was going to push anyone to do anything. E.g. some people wanted to dance, some just to sit and listen (we had an awesome live band, whose diary partly determined our wedding date ) And that was fine with us - as long as everyone was comfortable.
And to this day many of our guests still talk how much they enjoyed the evening.
The drama, however, was in the number of guests... where I come from weddings are family affairs of large scale, similar with Mr. O's side... and we just weren't going to have it. So, we invited only the closest and dearest members of family, and friends (friends *are* the family we choose, after all) and some simply could not stomach that they didn't "make the cut"... but their reactions made it perfectly obvious why they did not deserve our invitations.
Good luck... make it the least painful for you in the long run. That day, too, shall pass. In the end, the real life begins after the wedding.
ETA: I know what I wrote is about my wedding, not other 'supporting' events. The bottom line is try to make it memorable for you in all aspects you have control of. Some things you won't be able to control and I hope they'll be less painful than you anticipate.