And, there it is!
I've only got as far as this post, but from the OP, it has screamed bitter ex and parental alienation.
OP is furious that her ex has met someone who he loves enough to marry and to want to spend the rest of his life with in a family set up - and that person is not her.
None of this petty keeping the ex and his wife away from the children has anything to do with the child(ren)'s benefit, and is all to do with the OP's anger at the ex leaving her.
Since when, on Mumsnet (or IRL) has it ever been acceptable to limit the other parent's access to the children because of hurt feelings, if said other parent isn't abusive?!
The children absolutely do NOT "see the new wife getting better treatment than the OP did" - if they have any knowledge of that, it's because it's being fed to them by the OP.
Yes, the kids might be upset that their new half siblings get to live full time with dad and they don't, but (a) it hasn't been stated whether dad wanted more access and this has been kept from him or not, and (b) even if he did only want them EOW, the OP has a duty to the kids to cushion them from sad feelings about this, as we all do as parents to protect our children to the best of our ability.
I have sympathy for the OP if she is heartbroken after losing her ex (although after several years, and the way she talks about him, it doesn't really sound like there's any love lost there, it honestly just sounds like bitterness that he has moved on successfully and she has not), but after that update, my sympathy has withered and I honestly hope that the ex has good legal representation to stop this alienation in its path, and I'm not really surprised that he wants his wife with him whenever the OP is there, for support and as a witness to any confrontation that may arise.