danTDM the difference though is that you still encourage a relationship between your DD and her father. It is very clear here that the OP does not, and that she just accepts that her children don't want to see him or his partner or even to meet their new sibling. And the fact that she was an OW is going to make a difference to how the OP reacts, of course it is.
My DS was incredibly unhappy when his dad told him that his DP was pregnant. Also the fact that she moved in already pregnant and with her own DD who is with her full-time was a huge change and disruption to DS, and to be fair he has spent much less time there since. At fourteen I of course cannot make him go, and I never would. But it's still important that he have a relationship with his father, because even at fourteen it would be incredibly easy to let a relationship slide once you've not seen someone for a week, then a month, then six, then a year and so it potentially continues. And at fourteen a child still isn't mature enough to realise that cutting a parent off at fourteen means potentially losing a relationship with them into adulthood.
And what of the baby? Whatever anyone's feelings towards the parents in these situations, there are often children in the equation who didn't ask to be in the situation either. And who, as they grow up, will learn that they have siblings who want nothing to do with them specifically. Whatever your feelings are towards the adults, no child deserves to grow up in that kind of relationship. If someone posted here that their children didn't want to know their half siblings and would rather they didn't come to stay, no-one would be supportive of keeping the other kids away. In the same way no parent should support a child's desire not to meet their sibling. Not ever.
My eXH wasted no time in telling my DS that he'd always wanted another baby but that he'd tried for one with me but that we'd not been able to have one. No mention of the fact that it was him with the low sperm count, just the fact that he'd wanted another child. And yes, that stung a bit given we tried for six years for another baby and he seemingly managed to get his GF pregnant with an unplanned one (given the length of their relationship etc I don't think it was planned but obviously can't say for sure). And yet I have encouraged the relationship between DS and his sibling all the way. From telling him that he wouldn't really know how he might feel until the baby was born, how the way he felt while eXH's DP was pregnant didn't need to carry forward once the baby was born because feelings change. And they have.And I have taken an interest in his sibling. He was born with a genetic condition and has required surgery, and have encouraged DS to show interest, not that he doesn't, but he's a teenager and teenagers are not communicators as a rule.
It would have been so so much easier for me to agree with every reason why DS didn't want to stay at his dad's, or to simply nod and let him stay here with no dialogue as to the why's and wherefore's. But the reality here is that eXH is my ex. The fact here is that we loved each other enough once to have DS, and that still has to count for something.
As DS grows up he will form his own opinions of his father, they may be good, they may not, I suppose it will depends on a number of things. But whatever happens, his decisions are his to make, not mine to facilitate.