Hi NancyBee,
I would agree with QuietSong and Pen about stepping back from most or all of these issues regarding your daughter. They are going to drive you crazy, and you have no control over them. Here are some thoughts about some of the concerns you raised.
What your daughter chooses to do career-wise and education-wise is her concern. I'd stay out of it and let her figure it out. This relates directly to her money emergencies, and I would not respond to those either. She has made choices, and she needs to live with the consequences of them. How else is she going to learn? Especially when she has burned her bridges with her family after you all have done so much for her.
Regarding her staying married to the felon, I would let that go. We can't pick our AC's partners, but we can limit or eliminate our exposure to them. Your daughter, of course, can choose to let your GD see/hear from this man. I'm not sure if your concern is due to the nature of his crime, and surely that would make me extremely worried as well, but it may be totally out of your control. As far as the issue between the granddaughters/cousins, I'm wondering why the GD who was called "butch" in a text message can't get a new cell phone number? If there is bullying behavior at school, that can be reported to the GDs teacher or school principal.
As for the GS who isn't getting the help he needs to graduate on time, there are free programs (in the US) for students to complete their HS diploma or GED that might not take all that long. I work for such a program. In my school district there is lots of free support to help students graduate. High schools want to see each student graduate. As this boy is almost 18, he could meet with a school counselor to get information on his options himself. He should be starting to advocate for himself anyway.
Your daughter is right about one thing: her business should be private, unless it compromises someone else's safety, especially a child's. If you don't "know" her business, you can't be accused of taking sides. But the other side of that coin is that there should be no more handouts, no free shelter provided by family members, and limited contact. It must be tiring listening to her complain about the lack of fairness in her life. I've been reading lately about the "medium chill" technique, and it might be useful in your dealings with her. I posted it in the Helpful Resources section under the title "Loving Detachment 101."
I'm sure these are enormous struggles for you, but it seems as though you know the answer to your own question about your involvement and influence. It will never bring you peace to stay involved in trying to keep her afloat. I don't really know how to respond to your worries about your grandchildren. It is great that you have a good relationship with them. I hope that will continue.
I wish you the best in letting go of what you can. Most of us who have started letting go of our ACs senseless decisions and behaviors and started focusing on our own lives have found peace.