How can one deal with a brother who cuts off his parents and family when angry, and refuses reconciliation, believing that his parents' actions are wrong?

The rights of parents are immense; Allah has coupled them with His Own Rights. Righteousness towards them is an obligation that includes spending on them, obeying them in what is good, and showing humility towards them. Disobeying them is one of the greatest major sins. The disobedient child must be reminded of the gravity of their actions and warned of Allah's punishment, while varying the methods of advice, searching for the causes of their disobedience, and attempting to resolve them, without despairing of their guidance.