Welcome, Sjlll! My heart aches for you! I'm glad you found us and feel free to vent here. No doubt, you will get a lot of support.
It sounds as if there has been trouble in your family, unfortunately, for a long time. Your D has been difficult for a long time. Your ESDs (estranged stepdaughters) have "despised (you) for 25 years," for whatever reason. And your ES (estranged son) is bipolar, sadly, which I'm sure impacts his behavior towards you.
I'm horrified by D's stealing and her nasty vilification of you to everyone she could think of! Is it possible she is still "drinking" and "drugging" and that's what is causing this awful behavior? I'm no expert, but Ive heard drug addicts are very dishonest and will do just about anything to get money for their habit. That doesn't make this any easier for you and DH, I realize... sigh...
But I'm a little confused... after that, do you still see D's kids "every 2-3 months?" If so, I'm glad, but I know there must be tension between the adults.
Did the ones who say they "can't trust" you w/ their kids give any reasons? Don't get me wrong, I don't think you're untrustworthy w/ kids, I'm just wondering what in the world they could have said, especially after they have relied on you so much in the past.
I'm glad you have one DS (dear son) who is such a joy. And I'm glad there are other parents and kids who think so highly of you. Please focus on enjoying them, more than hurting over the estranged ones.
Please don't blame all millennials for your estranged AC's behavior though. There are narcissists and people w/ biplolar disorder in every generation. And remember, your DS and those other parents are millennials, too.