How can one convince a brother who is disobedient to his father, and who believes his father deserves such treatment, to stop his disobedience?

It is advisable to offer counsel to the father and brother in a friendly and gentle manner, with good admonition, as Allah Almighty says: "Invite to the way of your Lord with wisdom and good instruction, and argue with them in a way that is best." (An-Nahl: 125). One should vary the methods of advice and use everything that influences them, such as stories, encouragement, deterrence, and arguments. Furthermore, cooperation in righteousness and piety among relatives is important.