Am I in the wrong?

Every year you invite her op, every year you want your husband to spend it with you, every year you do the same for Xmas etc,

millions of people have coeliac disease, there is no need for your fear, there is plenty of things you can eat.

You did make it clear OP, the problem is that you seem to think it should dictate every special occasion for everyone but it doesn’t. You seem to expect all sides of every family to be there every time, and that just doesn’t work for everyone.

Absolutely, the op is even stopping her husband taking his mother out for Mother’s Day lunch, if he wishes lunch with his mother, if any of them do, it has to be at her house.

she sees it as accommodating them they see it as always forcing them to do as she wishes and never allowed to do something nice for their mother.

op, stop forcing every even to be at your home, you can eat plenty of things without risk of cross contamination, you chose not to.

But you can have a salad, you can have veg, potatoes, meat, poultry, eggs, rice etc, none of that risks contamination in any decent restaurant.

as said, you threw the bit in about your allergies at the end, but the issue is fundamentally you are persisting in not allowing them to take their mother out for lunch on Mother’s Day ever and then take offence when they do so.

this is the issue, either go with them snd eat from a list of safe foods, or say something like every second year its with you.

I do think you are in the wrong here although with good intentions. You see it as organising nice events for people while accommodating your food allergies. They may see it as"we are all supposed to go around there again". While there is no excuse for letting you down at the last minute, which is rude, you are not picking up on the clear signals they are giving you that they do not want to come to yours for these celebrations and are finding it awkward to say no, or thinking saying "something came up" is more polite than a straight no thank you we want to do something else.
This year they have said "no thank you we are doing something else" and you have proved them correct by being dramatically upset. Be gracious - not every thing needs to be according to your plans

As 1 of 4 siblings there is NO way we would all give up Mothers day to spend 4 hrs with our DM and each other, leaving mothers/husbands/children at home. I think its an absolutely weird situation. When you get married, have children your priorities are/should be for your 'new' family. My DM could be very controlling but even she would never have suggested this!
Before my DM died we would go and see both her and my MiL on Mothers Day, both live close by,
I would continue to offer with a ' going to have get together on [date and time] would love to see you. Let us know by [date] if you'd like to come' and Id leave it that.

I think the issue here is due to your food allergies they can never ever take their mother out for Mother’s Day, it always has to be at your house. And you won’t give them a pass ever. It’s with you, at yours, or nothing.

can you really not eat out at a restaurant ever?

What a load of hassle! I wouldn't bother from now on, it all seems a bit forced and unpleasant

I voted YABU as this sounds like you are verging into martyr territory.

Stop hosting and organising things for people who are flaky and treat you badly.

You aren’t responsible for maintaining a relationship with ILS, just drop the rope.

I understand they are being difficult, but does DH need to be with you every Mothers Day, can’t he have a year with his mum? He could spend the day before with you?

You sound like you are trying to organise and take over quite a bit of their family socialising. It sounds like they like to do their own thing last minute and it doesn't fit with your formal, well in advance approach. Sending an invitation for something they usually organise amongst themselves does give them a dilemma. I would say it is kind of a hierarchy issue - you are assuming that you are of equal status in their family hierarchy and that if you organise and invite first that gives you some kind of first dibs claim on the event. But that is not the case - they like to discuss and decide rather than one person taking charge with an invite. You should let them take the lead and stop trying to arrange things, then either fit in with them or not, as it suits you.

I don't think youre unreasonable but it sounds like you like to plan everything very far in advance. I know people like that too, they think they are being organised but it can come across as controlling.

Often people don't want to commit to plans weeks in advance and are happy to see how their weekend/Christmas/Mother Day etc works out closer to the time. This might be why you end up having people cancel because they had to say yes too early before knowing how everything else they have going on would work out.

I have in laws like this. They are actually genuinely really wonderful people but their concept of planning and organisation, especially for 'big' days, is just bizarre. The best/worst year was when we had mentioned Christmas back in August, they'd murmured about going away by themselves. We said well let us know, heard nothing. On the 22ND DECEMBER!!!!!! they sent a text to the family whatsapp group asking if we wanted to go out for dinner with them for christmas day lunch?!?! Firstly no weve had plans for months.... secondly where would even be available on 3 days notice?

Over time I've had to just stop getting upset about it. You, like me, wont ever truly know their reasoning. Maybe they're waiting for a better offer. Maybe they think youre an awful cook. Maybe they don't like something about your house. Or maybe, and much more probably, theyre just flawed weird individuals like the rest of us and this is their flawed weird thing. Set some boundaries about response times and planning, then just let them be their own unique weird selves and you do you.

You should also consider the fact that maybe the don’t want to spend the day with your family (your mum, etc). I’d find what you have described as full on and overwhelming. Even with people I have no problem with, it’s just all too much. You might like it but it all sounds quite controlled (even if you don’t think it is) and I couldn’t relax and enjoy something like that.

Your food allergies aren’t a reason for your mil and her other children to never have the Mother’s Day celebration that they would prefer. I feel sorry for your MIL that you can’t spare her son for four hours on Mother’s Day without it becoming a drama where you are ‘incredibly hurt’. Your DH would still have plenty of time in the day to support his children in celebrating you for MD if he was allowed to spend a little time with his own Mum. You are being very controlling.

I think every family has their own way of doing things, and obviously yours is very different from his family. If you already had plans with your family, that sounds like why they didn't invite you - not because they didn't want you there? But I also don't think they're necessarily wrong for not wanting to come to you every single time, some people just prefer a casual lunch out or something rather than making and hosting a big event, which is your preference. your dh turned them down to stay with you, which is good.

It sounds like you want to plan things and host because of your food allergies as it makes things easier for you. While this is understandable, you can't always expect DG's family to want to be at yours every special occasion. However, they shouldn't accept then pull out last min or mess you about. They should politely decline if they want to make other plans.

As hurtful as it can feel to be left out, it doesn't feel unreasonable for MIL to want the occasional Mothers Day just her and her children. If it was expected every year and meant you didn't get to have MD with DH and kids, that would be unfair.

I voted yabu because yabu to have made SO much effort for so long for these knobheads.

I suspect others voted yabu for this reason too.

Insanity is doing the the same thing repeatedly and expecting a different result.
DROP THE ROPE.

They don't sound like they want to go along with your plans so I would just stop inviting them and making so much effort.

Is there an element of doing the same thing yet expecting different results here?

What different things could you try? Would something more casual that doesn't need planning as far ahead work better if they can be flaky?

It sounds like you want to make a really big deal out of mothers' day while they're not overly bothered. In my family it's always been a 'send a card' thing as opposed to something akin to Christmas where you need to keep score of who's been where each year (and get all aggrieved at any perceived imbalance). I can well understand why they don't want to attend a state banquet hosted by and at the house of somebody who sounds quite stressy, but because you invite them long in advance every time you put them in an awkward spot. They do sound a bit flakey but take the hint - they're not that bothered and don't want to spend all day at your house for mothers' day.