Re: fact based fiction
Change the names and the locales and you're on safe ground. Anyone can sue you for anything, real or imagined, but if you change the names and locales they won't win in court. And if you stick to the truth, you're on safe ground, anyway.
Odds are just as high you'll be sued, even if you fiction isn't based on anything or anyone. All it takes to be sued is someone thinking the story is about them. Winning such a lawsuit, however, is darned near impossible. In order to be guilty, even if you're wriitng nonfiction, you have tell a lie, and you must do so in a manner than shows you actually intended to damage the person. If the lie wasn't meant to harm, then it still isn't anything that matters in court.
There is no law that says you can't write about anything or anyone at anytime, and you never, ever need that person's permission. All you have to be is truthful, and even if you lie it must be shown that you knew it was a lie, and that the lie was intended to do harm.
If writers couldn't write the kind of story you're talking about, half the fiction out there never would have been written.
If you ever needed permission to write about anyone or anything, there would be no newspapers, few magazines, and no true crime tales at all. No one is going to give permission to have negative things written about them.
The only real charge you ever have to worry about is invasion of privacy, and again, this is almost impossible to take to court unless you break into someone's house and steal information about them, or take their mail, or tap their phone.
Invasion of privacy only takes place if you break the law. Writing about someone using information you already have, or using information you can get through interviews or public records, is not against the law, and isn't an invasion of privacy.
Fiction writers have used real people in their fiction for centuries. It sometimes gets them in hot water with those people, and with friends and family, but it isn't illegal, and usually makes for good fiction.
When you start asking permission to write about anything or anyone, you're making a compromise, and it isn't a good one.
Making it up is fine, but good fiction is always based on reality, and good writers constantly write about friends and family and anyone else they happen to know who has a story capable of producing a good short story or novel.