Marital break up causes wedding dilemma

If the couple have received formal invitations it is up to them to decide whether they will attend, and I think the soon to be ex-wife should attend, and her husband.
People who have not been divorced do not understand how one becomes a non-person, illustrated here as the wife believes she is a friend of the family but the husband believes being a blood relative precludes her attendance. Comfortable friendships and the attendant social life can disappear overnight, as is happening here, and is amazingly painful.

I lost what were my only family ( I didn’t really have any family of my own) and also most of my friends when my husband and I split up. It wasn’t deliberate on their part but it just happens that way. Although no one liked the woman he left me for ( she eventually left him and went back to her husband) his new partner has totally replaced me and even though we only live a few miles away from each other none of them ever visit me when they visit him. I’ve made a new life for myself but it took a long time and wasn’t easy.

That sounds really sad Maybee70 and completely unecessary

Presumably uncle and wife were invited as a couple. The prime invite would surely be the uncle as a blood relative and his wife as the plus one so to speak. Since they have been invited as a pair they should come as a pair and not as two individuals. If they cannot come as a civil pair then they should not come at all. It is not their wedding day and they should be thinking of the young couple whose day it is.

It's up to the two guests to be cordial to each other if they both accept the invitation.
I would say nothing but have something prepared to mutter to them if either doesn't.

MayBee

Having an affair is abuse to me

There is for example, the lying to cover it up and the gaslighting when they make you think you are going crazy when you suspect things and they deny it.

Also affairs come with guilt and shame so often work will be done to blame you for the affair which can include mutual friendsand family which results in alienating you from them.

That's sad to hear Maybee and I can quite believe it
When I married DH I became part of his enormous extended family which I found a bit overwhelming as my only 2 cousins are in NZ.
I was welcomed with open arms and thought it was wonderful.
Then his uncle and aunt divorced and I heard his DG Dh gran say she'd never liked her (the aunt) anyway and proceeded to distance her and take sides
I never saw the ex wife again, though we tried to keep up with their DC
And I never felt quite the same about my wonderful new family. If they could close ranks so brutally over her, what would happen if I left DH 😔
I didn't but when there are DC involved this taking sides is horrible.

I am also sorry that this happened to you Maybee but I think there is another way of looking at this question of post divorce relationships.
If the non blood relative remains part of the ex's family and that family is their only social life, so to speak, it can prevent them from truly making a life of their own, and possibly meeting a new partner (if they wish to).
It is jolly hard work to start again after divorce, and could feel easier not to really try if the ex's family is still including one in the same way as if they were still married,

I am assuming here that all the children of the marriage are grown up.

Weddings are overrated

It is a very important event for the couple and very close friends and family

However, for others, they are an obligation and something you have to do

For others, something in the middle

The couple that is breaking up right now has rightly higher priorities compared to this wedding

Why not give them space?
This wedding dilemma, who will attend, will be solved by itself.

Leave it up to your Son and his partner to sort out. It's their day.

It was a long time ago. The only reason I bang on about it is that, prior to my divorce I used to see people get divorced and it didn’t seem to be a big deal eg Elizabeth Taylor used to get divorced all the time! But the doctors where I worked always took divorce very seriously. Then, when it happened to me I couldn’t believe how traumatic it was and, having joined a singles group that was full of fellow divorced people and hearing of their back stories I realised that it wasn’t just me. It’s even worse if, like me you stopped working to have children and had no career or pension to fall back on. And I felt as if I’d let my children down (still do). My partners son still can’t go back to the place where he first found out that his mum and dad were splitting up and my daughter has never really got over her fathers affair even though she’s the one that told me I had to divorce him because he would do it again if I tried to forgive him. She felt so betrayed. By the way, I don’t mean to sound so needy and poor me’ish! We all muddle along really well now. But I understand what other people are going through when it happens to them.

You don't sound needy or poor me ish at all Maybee you sound strong and resilient.

Thanks. Life’s a learning curve isn’t it!