Why is he over stepping his boundaries?

Ok, so my brother is 26 and his new wife is also 26. My brother works full time, his wife doesn't at all. His wife is a bit slow, but she could work if she wanted to. Anyways, her father is the real problem, he cussed my brother out because he claims he should be encouraging his daughter to get her GED, and to stop wasting her time doing nothing. I agree that his daughter does need to stay focus with school or getting a job, but he has no right to get mad with my brother because his daughter is goofing off. She spends her time just talking on the phone or going over friends has doing nothing, while my brother is working hard.