My father always manages to make my younger brother angry by calling him a failure, a looser, an embarrassment to the family. In the heat of the moment he calls our father a shayateen for always getting him angry. My brother always asks Dua for our parents in his thashahood in his prayer. How can I advice?
He’s absolutely sinful for calling such names and being angry with his father like this, it’s a major sin and he’s paving a way to hellfire as the parents are the gates to Paradise!
He must ask his father’s forgiveness and seek Allah’s forgiveness sincerely and repent. His father is sinful for being how he’s but this does not at all make it ok for the son to act rudely or even argue with the father.