I have posted in Step-parenting because there are 4 adults involved, but I am not a step parent.
I split from XH over 5 years ago. His contact then was 1 weeknight and 1 weekend night per week, initially only with the older 2 DC but after a while with all 3.
2 years ago he began a new relationship, 1 year ago they began co-habiting and this month their baby is due.
Since the introduction of his new partner, XH has apparently lost some interest in the kids, and could not understand their desire to spend time with just him, rather than with him and his partner and her family. This led to a lot of trouble, kids refusing contact etc. We went to mediation and I practically begged him to spend more time with them, set up Skype, email and text so I don't need to be involved etc. He now sees them for 2 nights per fortnight, with occasional Sunday visits for a couple of hours in the off weekends. There is zero contact between him and the children between these visits. They no longer even ask about him.
The new baby has caused some issues for my children in that they feel pushed aside already, before the child has even arrived. Now XH has decided that he does not want to have the children overnight for a period of 6 weeks from around the time the baby is due.
My opinion is that this is immensely damaging, my middle child is already refusing contact (he's 9, I have been advised by my solicitor that forcing him to attend is a bad idea.) I can't see the reason for stopping contact. I think the children need to be involved with the arrival of their new sibling.
I am dealing with all of the emotional fallout, my 11 year old DD feels unable to tell her father how she feels about anything as he gets upset. She feels responsible for that. But she feels that her SM does not like her, and does not want her around. She's a mostly delightful child (with periods of being a PITA as all children do). I try to pass on her feelings to her father, but he focuses on the fact that it is me telling him.
This was not an acrimonious split, it has only become so since he started living with his partner. I genuinely do not know what I did to make things so awful, but my older two children are really, really struggling.
My BF does not live with us, but is more involved day to day with the children simply because he sees more of them and helps me out with school runs etc. The children do not seem to be threatened by his presence; we often have family meetings (me and the kids only) where we talk about this sort of thing and how we all feel.
I need help, I don't know how to support my children through this upheaval and seeming rejection (I'm sure he's not really rejecting them, it's just that he's caught up in his new life I think.) Book suggestions or experiences would really help.
TL;DR - XH having new baby, kids struggling with fall out, help please.