HalleLouja, I didn't recognise the scene mentioned in 'Kate was also remarkably insensitive when Nathan mentioned the family being upset at James' death.' but maybe I just wasn't paying attention!
It was so contrived that they'd all suddenly go to Kate's book launch. Or had time passed in the interim (it often seems to in this show) and they'd all met her/spent more time with her than we've seen?
So is Zander's boyfriend (husband?) planning to leave Zander for Nina?
And is Ruth's husband really a) going to leave her and b) wanting Hannah to be his divorce lawyer?
Neither of those scenarios are messy at all... 
I thought Lennie was going to be coming out as trans and that's why she wanted a divorce. Wonder if she'll be persuaded to stay/tell her DH about her illness?
Saw the 'IVF' baby thing coming. While I know Hannah telling him to be honest caused problems, I don't think she did the wrong thing in a way; as she said, it was a bomb just waiting to go off and it might have been even worse if discovered down the line.
I quite liked Nathan this episode, for not being wet for once and actually standing up to Hannah a bit. I do think she's got a nerve acting like the wronged party when it's her that's been cheating.
Having said that, I like Christie and want them to finally get together.
Yes, I believe nesting is a thing. I think the rationale is that while the children are having a hard time, seeing both parents in familiar surroundings where they feel safe is less disruptive.