Fireworks pass @Faith-and-Hope , don't let him manipulate the situation. Some fights are necessary. You've suggested that he and some of his family exhibit NPD behaviours and thought patterns and their sense of self is very self focused beyond the average.....if this is true, I am hoping that after all these years you are able to see through it, and will be able to protect yourself if that ever happened, which I am hopeful it won't.
I read a post on the LE side of the forums about 'covert narcissim', and from my experience it is not covert at all, it is actually a more self aware narcissism, that often comes in the female form. I have mainly seen this in women, not everyone presents as a Donald Trump, and the only reason it is not as demonstrative and in your face is because they know they are narcissistic.
They over compensate for it by faking insecurity & a lack of self confidence to try and hide their sense of entitlement, play the damsel in distress to the n-th, but have very high anxiety because even this is inauthentic & put on for show. They get the jitters that peeps like me, with my past, see straight through these chicks, I don't fall for the self-doubting sham for a single second.
I think if your husband was to be self serving it would be pretty obvious and nothing covert about it at all. It sounds like he can have a short fuse sometimes and it would all explode instead of being an orchestrated plan to deceive & gets what he wants. Guilt will play a big part in the separation because he does genuinely love his children, and I don't think he will try and railroad you, but that doesn't help how you feel as an individual and as his wife, that its only because of the kids he is being considerate would really hurt....
Its natural to be curious if the other women knows him well, health problems and all, and wonder if their relationship has substance. I guess weather it works out or not may not be enough anyway. Maybe there has been too much water under the bridge for the chance of a future reconciliation.
It will be nice for you to get away and be really far away from the stress of all of this.
Corny