I'm sorry for all your losses, iamthird, your AH husband and the family connections, all the hopes you had for genuine roots with them all.
It is the nature of children to be self-centered, and I do not mean that negatively, it is just that it takes many years of maturity to grow out of the natural self-centeredness of childhood. And most children do not see the bigger picture, and they rarely give much thought to the adults in their lives if those adults are not their caregivers. I hope you won't be too hurt if your nieces and nephews seem to "forget" you. When they grow up, some may circle back to contact you and re-establish connection.
As for the in-laws, the sisters of the AH: you are building a healthy life now, you are creating a new life with good people who do not bring you down, and after the battle for your health you have fought, you have a right to protect your mind and your body from people who drain you.
I, too, think of people in my past who I had to let go because they were not good for me. Sometimes I ended the relationship, sometimes they did (which was my higher power allowing that for my own good). When I sit down and think it through, running it through my mind what the relationship was really like, and what it would continue to have been, I feel relief that the person is gone. Because I was always a "nice girl," there is a part of me that wants to think I should have been able to make every friendship or family relationship work. But I would rather be realistic than delusional! Being delusional has gotten me into a whole mess of trouble in the past, which is why I am on SR!