I don't turn in friends or family, for anything.
How about if your brother molested your three-year-old daughter? I mean, surely there are exceptions to such blanket statement?
I don't have a daughter, so it's difficult for me to put myself in those shoes.
But say it was my brother who molested my little sister, I'd prefer to handle it in-house. I wouldn't stop my sister from going to the police though, and would support her is that's what she wanted.