Fiancés Ex Wife won’t let my step son come to our wedding

I’m not sure if this is asking for advice or just ranting because I just feel at a loss. My (27f) and my fiancé (28m) are getting married this summer. He has a 5 year old son from a previous marriage and his ex-wife is a terror. She always has been, but this is a whole new level. We’ve been together 3 years and so I’ve known him since he was just 2 years old. We are getting married the Saturday of his first week of kindergarten. Please note that it IS our custody weekend, but due to travel and the rehearsal dinner, we can’t get him for the weekend on Friday night like we normally would. Instead, we arranged that my fiancé’s parents would pick him up at the meeting spot closest to his home on Thursday, and take him back on Sunday. That way, ex-wife doesn’t have to do ANYTHING in regards to getting him to the wedding. Except drive 5 min to meet his grandparents at the gas station. However, ex-wife of course won’t budge. She won’t even acknowledge that it is a wedding, she refers to it as “activities happening during our custodial time.” She said we could pick him up Friday night at the normal meeting spot. Of course we explained why we can’t do that. She also says he shouldn’t miss 2 days of school his first week of kindergarten. But really, it’s just a pattern of her regularly trying to keep him from us. She has not shown up for drop offs many times before, and she is always asking for some of his activities to be accommodated and my fiancé and I, not wanting to be the bad guys and wanting him to get to participate in his extra curricular activities, have MANY times missed weekend visits so that he could do things (like birthday parties, school events, etc). It’s too close to the wedding to go to court now, and court hasn’t helped at all in the past. She gets away with being a master manipulator and just so mean and terrible. We just want him to be at the wedding. It’s breaking my heart thinking that he may not be. What can we do? Bear in mind, too, that a year ago when she was having a baby, we missed some weekend visits because she wanted him there to meet his sibling. I like to think we are reasonable and would expect the same for her, even though she has never ever extended us the same courtesy. Just feeling very upset and at a loss.