AIBU to knock her head off ?

So they can speak up to him too. Maybe not in front of her… You said he was a wet lettuce didn’t you? Or they just don’t go round if she persists. They are adults and can say Dad she doesn’t need to tell us what she thinks about mum… plus they don’t need to tell you either. It sounds like the whole family is having a bit too much drama..

Your kids are grown ups. Stop getting so involved. People aren't daft.

I think what’s happened here is that your ex’s partner has become resentful towards you over the years because she would naturally have assumed that, as the kids got older all this contact you have with her partner for their sake would soon be ending as the kids outgrew that arrangement.

So now because they’ve got to this age and it still hasn’t happened, she is upset that the contact between you and her partner is still being engineered when there is no longer a need.

Instead of her showing maturity and voicing this quite understandable resentment she chooses to bitch about you behind your back instead. Your partner knows how she really feels and that’s why he won’t tell her to stop saying these things.

I think the wisest thing you could do now is completely stop having this unnecessary contact with your ex, who has been her own partner for years now which is why it hurts her, and then I bet that she will improve towards you once she feels more secure about your agenda.

The kids are adults now so you need to move on from "what the kids want".

Just be supportive and hear them and say bland supportive things like "I wouldn't worry about it, you know what's right" and "I'm sorry you keep being exposed to this but I'm not there and can't do any more than give you a hug when you're upset."

If they keep going then they'll keep hearing it. It would be better if they didn't relay it but not much you can do.

This sounds rough on them and on you (I'm not sure why you're getting a hard time for being pissed off you can't celebrate together if that's what you've always been used to). Have the kids said what they want to happen? I feel like if it was me at their age, I'd be cutting contact with my dad.

Part of being divorced means navigating birthdays and Christmases and each (ex)couple has their own way of doing it. But now your children are adults so embrace that and let them organise their own events. If that means two family celebrations we then so be it.
Likewise, if your kids have issues with their stepmum or their dad then they should deal with it themselves. Nothing, I repeat nothing, can be gained by you getting involved.

Then it is up to your adult children to suggest a way that could suit everybody
They could suggest going out for a meal altogether, where the 2 women who don't get on, don't sit together, or something similar.

What point is being missed? He’s married to someone who appears to dislike you, so it’s time you moved on.
Your kids are past the point of needing to spend their birthdays with their parents anyway, surely? And plenty old enough to understand why they’d be meeting you separately, for sure.
It’s frankly bizarre that they’d find that weird. I suspect it’s just you projecting.

I agree with you. It is as important for separated parents to be able to be in the same room together as young adults, as young children. The safe environment you created to make sure your kids never felt conflicted at family events being taken away by a silly immature woman would infuriate me. I'm like you - I have an amicable relationship with my ex, a couple of times a year we go out for dinner with him and his new wife without our adult son, and it's a point of pride to both of us that our son has never had to compromise on birthdays or at Christmas, his graduation will be a joy, his wedding a breeze...

So I get it.

And the fact she's actively bad mouthing you is infuriating. I would directly call her out on it. Plainly and calmly. Describe the situation before she came on the scene, and how things are now, and say it is a crying shame and embarrassing that you can't be adults in the same room for the benefit of the kids any more, and shameful that she bad mouths you. You bear her no ill will, you have no designs on her husband - you just don't need this drama, please stop.

She can't hate you more than she does, right? But if your ex is a wet wipe, you need to stand your ground if she's badmouthing you to your kids.

You sound like a drama queen who likes to have issues.

Your children are adults. They could choose to go zero contact with the other woman if they choose to. You are in exactly the same position. Just refuse any contact with her. You dont even need to be in communication with the father if you choose not to.

Move on. Your children can choose to move on too.

There are going to be plenty more situations in the future where you dont like how someone interacts with your children. Use this as a learning situation for everyone to deal with it like an adult rather than to knock someones head off

Precisely.
It looks like you’re looking for any reason to have a fight. Just don’t.

Telling them to ignore it is the right thing to do, but useless if you are reacting to her comments. They will get upset knowing that you are upset. The fact is that she is badmouthing you, and I suspect she's called you a lot worst than a fraud. Your adult children are old enough to tell her that they don't like it (tell their dad the same) and decide how much time they spend there. I personally would get up and leave the moment she started and would make it clear I was going back until she stopped doing it, but that's their battle. I know she's talking about you - I'm guessing things aren't great between her and your ex, otherwise she wouldn't be so preoccupied with you. The party thing is fine - you're divorced, celebrating together is nice but not essential. If your ex, his family and your DC desperately wanted it to happen, it would regardless of what his partner said - so sounds like the arrangment came to a natural end.

The fact you can 'jokingly' say shall I knock her her head off doesn't paint you in a particularly good light. Your children are adults and kindly, can fight their own battles. Its not difficult for them to tell their step-mother that they don't want to hear nasty things said about you. If they are firm and consistent in that she will stop. I'm the meantime, I would suggest focusing on yourself and not letting what other people think about you bother you.

Agreed. Work can be very good for your health and give you new things to focus on. It could be voluntary work to start with.

Look I hate my husbands ex, she’s a massive twat but nothing gives me more satisfaction than completely ignoring her, it really winds her up. We simply act like she doesn’t exist.

Most of them are just putting up a front for the children. And good on them for putting children first. Some were never really that invested in the first place. Don't compare your life to others.
You need to move on. Ignore her. Be grateful for the fact your children obviously don't believe her anyway and as for your ex mil still liking you, we'll isn't that a win for your side? Most people seem to have trouble with mils even when married.

Time to remove yourself from their lives, no need for joint events at their age!

If you believe you have the moral high ground, don't do anything which might compromise it.

Your adult kids need to manage their own relationships. You’re probably not the most appropriate person for them to confide on this particular subject, given you have emotional involvement. Ignore. Enjoy your life.

Then they should stop seeing their father if he won’t stand up for them. That is their choice. Tell your kids you don’t want to hear about what she says, and if they don’t want to hear it, they don’t have to either. Same with birthdays. If they don’t want two parties, they don’t have to attend two parties. There is no law that says adult children have to see their parents if they don’t want to.

Your kids are adults. Get a therapist.

But you ‘dgaf!’ you said!

It would be nice to get along but you don’t and aren’t going to by the sounds of it. Given the abuse I’m not sure why you would even want to be around them.
You know it’s not true and so do your adult children. They need to not respond to her when she’s saying things about you- grey wall. Who do they live with?