I think DH is being (a bit) U to MIL... AIBU?

She had no right to invite anyone. It's your house you do the invites. Sounds like MIL is the problem here.

He offered an alternative. I think you have to back him.

why does she bring someone so often? Is she uncomfortable with the dynamic too?

His mum, his boundary. You’ve combined let her walk all over the pair of you for years. Now dh has found a nice shiny spine.

It’s ok to have boundaries but I think he should have been honest about the reason he doesn’t think having Lulu there would be a good idea. It’s a bit lame to say it’s because of the kitchen when it’s just one extra person.
Having said that, it’s rude of MIL to just invite whoever she fancies.

But the fil has dementia and won't be able to cope with a stranger in the house.
The op's DH is not saying no because they are uptight. They are saying no because his ill father won't be able to cope.
If they said yes then they would, in effect, be excluding the child's grandfather.

I agree with him too, he's finally putting some boundaries in place - sounds like it's well overdue.

I also think you should support your DH here. Your fil can't help his condition and it may be one of the last times your DH gets the chance to share something like this with him. Why on earth would he allow someone else to take that away for no other reason than she wants her own way?
Your DH has offered a reasonable solution, it's his mother who is being unreasonable. She has to live with the consequences.
I would also think your DH needs your support as his world is changing and he will be doing the best he can to deal with both his parents in their new normal.

It's uptight to have boundaries? Your relationship with your dad is obviously not the same as the OPs husbands relationship with his mum and that's fine. She doesn't however get to just make unilateral decisions because she's his parent, he is allowed an opinion.

Wow I can’t believe all the messages saying your husband is right to say no. If my dad called and said he had my niece staying and could he come along with her as well I’d say of course and think nothing more of it! People are way too uptight these days!!!!!

Ok, the other DC then. Would they want their granny to be at the birthday celebration or won't they mind either way?

You need to back your husband up on this one. He is setting boundaries and you need to support him in doing that. And in case you’re tempted, absolutely 100% don’t go behind his back to mend fences, you will be showing him he can’t depend on you. Just stay out of it when you’re not asked about it and support him when directly asked/involved.

It’s their first birthday.

I think you need to absolutely support him. It's about her never hearing the word no and now she's basically throwing a strop because she didn't get her own way. Why would you pander to her tantrum?

She would rather lie and prioritise this distant relative than spend time with her son and grandchild because he dared to say no for once. Poor bloke is probably quite rightly at the end of his tether.

Support him in this or she will never adhere to any boundaries going forward because she will know all it takes is a tantrum and some emotional blackmail she will get her own way.

DH got it right and you should support him.

I’m strongly #teamDH - your MIL sounds like an overindulged horror who needs reining in.

Well, she might start getting it if she cares about the consequences of trampling on your dh's boundaries.

Am also with your husband on this. I do think he should tell her that his concern is primarily about how his dad will cope, but the conversation about uninvited guests is long overdue.
Some people might be all chilled about it, but bringing uninvited people to someone else's house changes the dynamic, it is rude and mil's insistence is her saying that she doesn't care about your dh's opinion - she's going to do what she wants, regardless!

Unless there is no chance of FIL attending I think DH should stick to his guns.

Your MIL seems to care more about saving face with her friend then being present and supportive to her son and grandchild on the child’s special occasion, which is hurtful, so I’m with your DH.

I agree with you that DH should have brought it up before and it does seem harsh to double down so strongly when MIL had no idea it was a problem, but it doesn’t sound like she’s have listened before anyway. And she’s rude to just assume that she can bring randoms to your home.

For me the deciding factor would be whether DC wants MIL there? It's their birthday so if they would be happy to see MIL then I think that's the important thing.

If it's been annoying your DH for ages he should have told his DM much sooner, he's blown this up into a bigger argument than needed by letting it go on and on. Leave him and MIL to make their peace or you'll end up getting the blame from both sides Op

His circus, his monkeys.

Life is too short. Id much rather have my mum there alongside her cousin who's visiting, than not have my mum there at all.

So many people on here have a stick up their ass when it comes to "boundary setting" with relatives. Just live and let live, it will hardly make a bloody difference and we dont all need to be so closed off to being charitable or flexible towards family members.

Back in the 90s people had such a different attitude towards hosting, we've all become so closed off

Your husband will be really upset I would imagine as this shows how little she thinks of him and her grandson or cares about seeing them and how emotionally immature she is. Which he probably knows but it’s been really pushed in his face when usually he can push it to the back of his mind.

it’s incredibly rude to invite other people to things, and emergency maybe where she was caring for a child and couldn’t leave them and it was a one off. She’s just probably amazed that he’s pushed back and will feel very affronted . Good for him.

Your husband knows your MIL better than you. Let him handle her how he sees fit and you have his back.