I wrote many stories about "Asher" and I always asked permission from his parents. I was pretty sure that nothing I said would alarm and offend them and that turned out to be true.
And, of course, I changed his name to protect his privacy.
I think that if you tell the truth and are respectful, people are usually okay with your writing about them.
That being said, I'm a writing coach -- I help writers improve and publish their prose -- and one of my clients, who isn't an Orthodox Jew, has written a novel that will be published by Penguin Books next year, with a protagonist who is an Orthodox Jew.
So we'll see how that goes.