My granddad’s sister was married with a kid, but had a lesbian relationship on the side for most of her adult life. Stayed married to the same guy 40+ years, affair was with the same woman almost as long. Worst kept secret in the family… everyone knew but no one talked.
My grandfather – abandoned his wife and 2 children, because he was more evolved than they were and so needed a more evolved mate (who was 25 years his junior). He paid no child support, leaving the state so he would not have to. My grandmother went to work as a teacher to support her children when she was 48. Because she had graduated from high school she was qualified to teach elementary school – she went back and got her bachelor’s in education when she was 54 so she could keep her job and keep food on the table. Grandfather could not understand why his kids, by my grandmother, didn’t want anything to do with him when they were adults.
My father was the black sheep of my family. He never broke the law or abandoned anyone but he was an alcoholic and so was looked down upon. He didn’t work for many years because of his alcoholism and concomitant mental health problems, so that gave them even more reason to despise him.
When he died, I kind of inherited the title. Not that I’m an alcoholic, work-shy or mentally ill but I must be a crap person because of who my father was. So, no family to speak of because of the black sheep thing.
Younger cousin on my mom’s side - heroin addict, sired at least three kids and doesn’t take care of any of them. Some prison time, stole everything from Grandma’s house that wasn’t nailed down while she was going through dementia and before she was sent to nursing care, because he was “helping out” around the house. He’s never invited to family stuff. Once he showed up anyway, and I was fairly shocked at his appearance, 10 years younger than me, looks 10 years older and missing most of his teeth.
On my dad’s side - my stepsister. Got up to some serious hijinks after high school, she was a year behind me (8 months younger in age) and started college but was asked not to come back by the school. Got involved with some skeevy people, enough that my parents changed the locks on the house, she got pregnant and disappeared for 10 years. When she showed up again, she was welcomed back with open arms, because that’s the kind of people we are - unless you pull the shit again yet another 10 years later, leave your son and husband holding the bag, and move a couple thousand miles away without a reliable address. She’s been written out of step-dad’s will.
I have another one.
My great-grandfather, the minister, left his wife and her 5 children for his mistress. Then, he called whatever the equivalent of child protective services was back then, to report her for not being able to raise her 5 kids alone.
They came to pick all the kids up. The only one they didn’t get was the youngest, still in diapers, which my great-grandmother refused to release, holding him in her arms. Later, she attempted to bash her own head in with a brick so the kids would get some money from it. She was stopped by her children.
There’s more but it’s not to do with the black sheep, more to do with my grandmother, who would nail you to the ground with her eyes due to the experience she had during this time (she was 12 when taken away and got expelled from the school about a year later for smacking down the principal to his face). And she never grew over 5 feet.
Eventually all were reunited. 
I had a great uncle who was a real piece of work. He dropped in and out of his family’s lives (and he had several kids with his wife), and when he was absent he was committing fraud, forging signatures, and failing to keep jobs.
The kicker is that during the last of these spells away from his family, he died in a boarding-house fire. Trying to save a lady’s cat.