Welcome to Psych Central, citizen of Ohio! I appreciate the time you took to be clear about your experience and feelings, and no, this was not a long post, but people nowadays hate reading, and you know that, so that's why you apologized about the post being long. Correct me if I'm wrong, though.

First of all, I'm so happy that you have beaten cancer! Second of all, I don't know what to do with that kind of people, other than a session of tough love, which won't be helpful since they will keep going, to avenge you or something, even though they attacked you first. Try to get back at them in a not so devastating way just to show them how this feels like, what they put you through. And then start talking with them about that, and if it doesn't work, then I really don't know how to help. I haven't encountered such species, ever. I know that what's keeping you on your feet is your daughter, and your nephews and nieces, so have them in mind and come up with a brilliant plan in order to get the family back together again, make that your duty. I'm not saying get your brother to divorce his wife, but show him what she is really doing to the family, and forget that you have depression, because it is clearly tying your hands behind your back, making you feel that you are less than an average being. The fact that you have beaten cancer means that you are stronger than you think you are, so have that horrible experience in mind in order to proceed, and the horror of finding out that you have cancer in the first place and you actually handled that, means that you are indeed strong.