Partner's children ignore me/ don't want to know myself or my children.

I don’t think there is anything you can do. This is between your DP and his DD. It sounds like she has given him an ultimatum and he has chosen you and it sounds like he will continue to prioritise you.
It sounds like you and your DP have a good relationship, focus on that. If he wants to mend his relationship with his daughter and that side of the family that is down to him. I would stop trying to meddle if I was you .

Eh, there seems to be a lot going on here. She may have a superiority complex about her wealth and the display of it, but equally there are those that have a superiority complex based on how much they don’t care about money/botox/materialism, and end up making it their entire personality.

It’s hard to tell if she’s reacting to you being ‘poor’, or reacting to your attitude towards her (which does come through very clearly). Or if it’s vice versa, or a combination of both.

For whatever reason you clash. Just step back and leave her alone. Her relationship with her father is between them, it isn’t something you need to be involved with.

A manifesto? Is she quite well??

I don't think there's anything you can actively do to improve things. Anything you try will, I think, be twisted by the daughter who seems determined not to like you. She sounds vacuous & cruel and maybe you have, inadvertently, let her see that you think this. I'm not blaming you, I wouldn't be able to be in her company for 10 minutes and it would be obvious why. I couldn't hide how shallow I think she is.

The problem is, if you have let her know that you see through her facade, when most people either don't see through her or pretend they don't, then you will always be her No.1 Enemy with all the stupid drama that that label implies.

And there's nothing you can do about it.

I don't know what to suggest since it's so badly affecting your partner's family life. He thought she was ethereal, clearly bought into the goddess-like personality that she fakes. I guess he has a tremendously difficult decision to make. I'm sorry this is such a rotten situation.

Im guessing this is why he has been single for 10 years.
His not so dd scared anyone off who may have been interested.
Id stay well clear and let dp deal with it. You cant change her or her entitlement

I wouldn’t be trying to do anything in your position, just stay out of her life and get on with yours. She sounds like a spoilt drama queen. If she can’t be polite to the person her dad loves and would rather cause all this upset for him then she’s incredibly selfish.

Honestly OP, I would be reconsidering this relationship. Or at the very least have a talk about the situation with your partner. Is he genuinely happy to not see his family ? Yes, his daughter is hideous, but will he be happy in 5 years to know he’s missed out on his grandchildren’s lives?

It sounds incredibly tough.

You don’t like his daughter, and are scornful of her lifestyle and values. You have told yourself that you are wholesome and ‘live simply’ and whether you admit it or not, see yourself as superior to the daughter who you clearly view as shallow and vacuous . Similarly the daughter doesn’t like you- either she’s read your vibe or has another issue.
This is irrelevant. Your boyfriend doesn’t need to choose and can have a separate relationship with you and his kids. He needs to grow a pair and tell you when he wants to go out with his kids, instead of hiding it like the family dinner.
Dint try and fix this, but encourage your db to have some integrity and maintain a separate relationship with his own children

Are you for real? OP is just trying to get along!
The hideous daughter has written a MANIFESTO declaring she won’t have anything to do with OP

'I value kindness above all else'. Genuinely kind people don't say stuff like this, and they definitely don't follow it with several paragraphs negatively judging another person's lifestyle, whilst acting perplexed about the person's dislike of them.
If you love your fiance, and want what's best for him then encourage his relationship with his daughter. It doesn't have to include you. Don't make him feel bad about it as if he's fraternising with the enemy. It's his daughter, and if he is already saying things to you that put her down it's because he thinks you want to hear it.

My adult children don't like my partner, my daughter in particular. She can't really explain why, and I just accept her feelings. I never thought we would be a big happy family. Why would we, he's a stranger to them. They prefer their dad. I tend to go to family things without my partner or arrange things when he's away. He's not overly bothered and it's much less stressful. There was a period of time when I did try to create situations where they met but it was very awkward and I stopped. I suppose the difference is that my children are civil if they do see him. That may be the best you can hope for OP, but how you get there from the situation you are in now I'm not sure. Perhaps suggest he just arrange a meet up without you?

You’ve said several times that you want to fix things, but there’s nothing for you to fix - that’s your DP’s job, if he wants it. He can ask his daughter to meet and talk about her letter so that she can explain what she actually means about needing boundaries because she feels unsafe around you, and dispel any inaccuracies she might have about you. He can meet with her and his grandchildren alone, as they’ll have done all the years he was single. He can make it clear that you and she don’t have to like each other, but if there’s an extended family dinner where partners are invited you’ll be attending as a couple and she can choose to sit several chairs down if she wants to. If your DP genuinely has no idea where all this is coming from (and being cynical, I suspect he knows / has been told more than he’s letting on but would rather stick his head in the sand or spare your feelings than tackle it) he’s being startlingly unproactive about addressing the complete disintegration of his relationship with a daughter he’s had a great relationship with before meeting you.

My ex’s dad married a woman in later life who neither he nor his siblings liked, and it was just quietly agreed that they maintained the same relationship with their dad as they had done while he was single, meeting him alone for a drink or lunch every couple of weeks or so, and exchanged pleasantries with his wife if they all had to meet at an extended family event. They were all adults with their own lives, they didn’t need to be a big happy family.

You’ve mentioned having a troubled family background and experiencing little love or support growing up, and maybe this manifests in behaviours which some people can find unnerving and uncomfortable, like overly investing in trying to make everyone like you, or over-involving yourself in the family, and a hyper-fixation on “fixing” everything. Only you know whether that’s a tendency you have. But you need to step back here, and put the responsibility on your DP.

Reading between the lines, is your partner older/ wealthier than you? Is there a difference in cultural background?

Also - and sorry if I missed it in your very long OP - did you have anything to do with your partner separating?

I would say - let it all be your partner's/ his kids problem. Dont get involved, unfollow and block her and everyone else from that side on Instagram. But make sure you are financially protected in case he dies, and be prepared for his kids trying to leave you with nothing.

Would it hugely upset you for your partner to go to a family meal without you?

If not, I would encourage him to go to stuff like that still and to continue seeing them. The last thing you want is for them to feel that he has chosen you over them.

Given the financials that you have outlined, I’d also make 100 percent sure that your children will inherit from you and that there is no possible scenario where his kids can end up with a large lump sum if you inherit from your dad.

Lordy. A manifesto?
Your DP is being very brave here. He's called out her trying to isolate you and she's furious.
Maybe the two of you don't get on, not the end of the world but this is quite cruel of her.
Maybe she's threatened or jealous - maybe it's around money or attention. But this is perhaps the downside of her having been more indulged than most as a child.
All your DP can do is continue to offer her his love, but not capitulate to unreasonable demands and you should probably keep out of it.

Good on her for knowing her boundaries and enforcing them. I wouldn't want my dad's girlfriend trying to be buddy buddy with me either.

If you don't think it's a genuine post shouldn't you be reporting it rather than making comments like this on the thread?

She was expecting my partner to go for a family meal (17 of them) but leave me out. He didnt tell me at the time but refused.

So some of his isolation from his family is down to him. He made his choice, now they have made theirs.

You clearly don’t like his daughter. She clearly doesn’t like you. We’re only hearing your side but ultimately it doesn’t really matter. You’re both adults. You don’t have to like or even accept each other or have any contact at all. But your partner should consider making some effort at a compromise where he sees his daughter and grandchildren without you so he can maintain some sort of relationship for the sake of the DGC.

It looked a bit like a novel…I’m amazed so many people had time to read and digest it. I thought most people on mumsnet were too busy running their kids to 72 afterschool clubs, making hand made birthday cakes, hosting baby showers, having their roots coloured or fighting with their step-siblings over inheritance!

Is it as simple as she's worried about her inheritance which shows itself as antagonism toward you? You tried OP, its sad I don't agree with others about 'adult children' in a better world you'd have all got along and increased general familial happiness...sadly she's crushed this ...grieve that for a bit...then move on and build on your personal happiness. Congratulations to you both 🥂

I'm guessing she sees you as a gold digger and thinks your children will sponge off her dad. You clearly don't like her and she doesn't like you. It's up to your partner whether his relationship with you, or his grandkids is more important, only time will tell..

If I were you I wouldn't want my children anywhere near here or the whole family.
Forget about her.
Your post is hugely about her.
She's ghastly.
He's raised a ghastly controlling woman.
This will NEVER resolve itself.

Move awayvand accept what you cannot change.
Put your children first.

If you haven't time to read it why not just move on?
It was actually a very well written, articulate post.