Sorry about your brother. The best thing for him is to make sure he isn't afraid of Rupert or he'll end up being afraid of dogs for the rest of his life. Sounds like an accident. If I had a whistle blowing in my ear, I'd snap too. Also, Rupert probably had no idea why you punished him.

Has Rupert had obedience classes? I know a place in NH that has obedience classed for dogs & kids. Maybe there is something in your area and you & your brother can take him to obedience class. That may help your brother be more confident around Rupert & not cry everytime he sees him.

Good luck.