I don’t think that person A doing jail time will cure your problems. It might make you feel better for all your anger at person A, but it will not make your life more stable. I don’t know what your relationship is to persons A through F (or whatever), or if you are one of those persons, but clearly you are affected by them in some way.
If person B is under person A’s thrall, and has remained so for decades, it is unlikely that person B will change. The only thing that might help is if person B gets therapy, or a job or both. Otherwise, you can’t force people to get help. You can beg them to, however, and if you do it enough, person B may eventually do it to please you (if not to help themselves). That’s not the best option, but at least you’ll feel like you’re doing something.
Otherwise, if the kids are being criminally neglected, you can report them to social services, and see what happens. Still, I wouldn’t want you to do this unless you are at the end of your rope with anxiety. You have to continue to talk to person B, and express your concern, and urge them to get help, and make it easy for them to get help if they decide they want it. Otherwise, I’m afraid, there’s nothing you can do.
So be there for person B. You might also occasionally urge person A to get help, too, although it seems like that is pretty unlikely, too. I have been in this situation before, and am somewhat in it now, and know other people who are in it. It is good to be caring, and most of us are caring, so it is very difficult to see people we care about be hurt. However, we can’t do a lot except be there to support them.
Some people may believe in stronger interventions. I am skeptical about those things, but I suppose they might work. It’s not my style. I prefer to work people until they choose for themselves to help themselves. I try not to get attached to the idea that I may succeed at getting them help. I’d be even more of a mess than I am, if I got frustrated all the time that I seem to be unable to do something.
So, care. But maybe from a little more of a distance. Share your concerns with other people who care about all these persons. It helps to talk and vent and sometimes you can get new ideas. It also helps if more than one person is giving all the persons the same message.
The kids will survive. It will be harder on them, but not as hard as being kids in Rwanda or Somalia. People grow up. They are damaged, but they still have lives and may still find moments of pleasure. You can’t make everyone’s life perfect. Just having life is still a gift, even if there is a lot of pain in it. That’s what I told myself every day, when I was considering giving up this gift. But that’s neither here nor there.
Care. Try to put a little distance between you and your cares, because you can’t control things, and you don’t want to get burnt out on anxiety. Find others to share your concerns with. And hope! Hope, hope, hope!