You think he is paying the entire mortgage for his older children's house that is jointly owned with their mother? Seems highly unlikely. 🤣 Happy for the OP to correct us if that's the case but her posts appeared to imply it's still jointly owned and he has continued to pay his half of the joint mortgage since leaving because it is his children's home.
Children don't require a room each for short visits to a non-resident parent. Again, OP's posts imply the older children live with their mother and just visit their father, hence him continuing to fund the costs of them being raised in their home with their mother.
She has confirmed that this was all in place before she decided to move in with this man and have another child with him. She's also confirmed that - despite these existing financial commitments to his older children that she was fully aware of before deciding to move in with him and have another child with him - they can still afford to purchase a house with plenty of room for their new family unit.
However, she'd like to force the older children to move to a smaller home so she can have a larger one than them, and she resents ger partner paying his share of the costs for raising his older children because it means she can't have the size of house she'd like to buy, without forcing him to reduce the financial support for his older kids so that they have to leave their home, which sounds like the one bit of stability they've had through this shitshow in their early lives.
I'm not sure I can imagine a much more selfish way to behave towards young children who've already been through a great deal in their early lives, than to propose this not because it's necessary but just because you want an even bigger house for yourself with bedrooms that will sit empty much of the time.
Horrible. Fortunately, it sounds like her partner is not amenable to her attempt to validate all of the worst stereotypes of stepmothers from Cinderella etc. 🤣