To be hurt that MIL won’t attend our wedding?

This. It will be their loss of beautiful memories they could have shared with you both. I'd be polite but no longer go out of my way to meet up with them or send gifts for birthday and Xmas.

Ignoring the rude SIL and concentrating on MIL - is it because she would be alone? Does DH have aunts/uncles, cousins - long standing friends of the family attending that she could sit with? Is she worried about getting there feeling awkward if you have a big family
Does she have a close friend or neighbour that could accompany her?

I would make a final attempt - call her and say how sad DH is that she has decided not to attend his wedding. Tell her that you are sad as you thought the two of you were close but this is telling you otherwise. Maybe speak to the pregnant sister and tell her how upset your DH is -perhaps she could persuade her

If your MIL still refuses, I would dial down the relationship. No copies of the wedding photos or video. No details at all. I wouldn't be at her beck and call either. DH would be visiting on his own for a good while. No invites to dinner/BBQ's if they chose no to attend the wedding without a good reason

Do you think MIL won't go because she won't know anybody there given that BIL and SIL aren't going either? Or will it be a long way to travel? Involve an overnight stay?

She objects to your marriage in some way. Probably can’t stand the thought of her son moving on and having a different family. Same with SIL. Bizarre to just not attend the wedding of such a close family member.

MIL’s reasoning bit out of whack 🤨. FIL didn’t live to see any of his DC marry, so she won’t see her DS marry either, even though she’s alive? Did she go to her other DC’s weddings. Perhaps she feels a bit wobbly coming on her own. Could you suggest she brings a friend or another relative and make it easy for her to stay over etc. At end of day, though, your wedding should be a day for you to party on down. If people can’t/won’t join you, their loss. Enjoy!

My MIL and BIL chose not to attend our wedding. She used the fear of getting Covid as an excuse even though lockdown was long over by then, and there was really no excuse for my DH’s brother not to come, other than his social awkwardness.

I just can’t understand why she didn’t want to be there. She was only thinking of herself and I was so upset for my DH to have no family there on the biggest day of our lives. I find it very hard to get past and haven’t spoken to or seen her for more than two years.

I really feel for you. I would tell your MIL how upsetting this is for both of you then go LC if she doesn’t turn up.

I can’t understand their logic at all.
Did they expect that you’d consult them about the date but you didn’t? I’m clutching at straws here as both MIL and SIL have produced really batshit excuses.
I don’t think you are close to your MIL . You are probably nice and chatty and she goes along with it as it suits her but that’s all. She put you on your place from time to time deliberately, it’s a power play on her side.
She is probably not happy that you’re getting married maybe because now your status will change officially or maybe something else.
Is SIL married by the way?

I don't think I'd care if I made waves, they seem to not care about making waves themself anyways.

For your brother's wedding? Weird.

Not for a sibling's wedding? 🤯

Oh wow, what an uncaring family

I hope you and your partner have a wonderful day without the miserable, weird fuckers

The next time MIL asks you to do something tell her it will be too difficult.

Your MIL and you aren't close, you are just more entertaining than her son is to her. They have no bond.

This is great to face now as you can prioritise you and MIL can just be a someone you know of. If you DH wants to see her, buy her things, whatever, let him crack on without you.

How utterly insane. What can you do but just smile and go along with it.

My mother attended my wedding three months after my stepdad died. Honestly OP, YANBU, and I can't fathom how anyone would chose not to attend her son's wedding for any reason. Also SIL is BVU - I can't imagine anyone not wanting to take a day's leave to attend their brother's wedding. DP's brother is the only one with a valid excuse. They sound beyond weird tbh. I would be cooling off my relationship after this, it really is not on. If they can't make an effort to go to their own son's/brother's wedding then I would be making little effort to have anything to do with them.

The trouble with being ‘part of the family’ is that in some families the parents aren’t that interested in one or all their adult children’s lives You’re the one who makes more of an effort with your MIL but she’s also doing this to her son who is blood.

When you say that your DP ‘doesn’t seem overly bothered by it,’ I’d wonder if he’s just accustomed to it. He’s had a lifetime of this.

Could it be her grief getting in the way? You said she expressed it was because her husband died and would be missing seeing his children get married. Maybe this has hit her, something else she is missing doing with her husband? Was there anything included in the wedding day to mention her husband or being his memory into the day? Big life events can bring raw grief up again.

You wouldn't take a days annual leave for your BROTHER'S wedding?

This. Putting an 'it doesn't bother me' face on is good. I wouldn't keep on seeing your MIL more often than her actual son does anymore. Cut that right out.

Wow, not to see your brother get married?

I presume it's a naked wedding?

My family are like this. Just plain old mean. Years of striving for a relationship and repeatedly hurt by similar actions to your MIL/SIL, questioning what I've done and if I'm wrong. Last few years I've stopped initiating contact and they have never contacted me. It hurts.

I think his family are batshit … however has your Dh to be been able to stand up for you or him in other situations as this would worry me .

I would not waste my time on someone who didn’t want to come to my wedding

@SatsumaCat your MIL is awesome. Does she run classes in how to be like her? If so, sign me up!

Only the brother who’s expecting a baby has a decent reason. Not wanting to take annual leave is pathetic. The MIL is even weirder, especially as you’re close. Pure speculation, but is the fact that you’re getting married now too “real” for her. When it was just a relationship her son could easily walk away from it was okay, but this is too much? Is her own daughter unmarried and she resents that you’re getting married before her? Is she someone who likes the attention on herself and doesn’t want to give that up on your wedding day? I also bet your DP is much more bothered than he’s letting on, but it would mean admitting his mother (and sister) are being nasty sods.

Yes, I mean, did the OP and her DP just say ‘Oh well, fine — pass the salt, please’? And when you told them you were engaged, they just said ‘Lovely weather for the time of year’ and never mentioned it again?