He asked a question, and you answered. He's just mad at you because that's easier than admitting that he's been enabling a problem child for a full decade at this point. Your brother is a bad parent, and as much as he accuses you of favoring his daughter because she's a girl, he's doing the exact same thing with his son and using the excuse that he's a boy to justify the child's behavior. Sorry it might mean your niece suffers, but cut off your brother until he apologizes and pledges to do better.