What is the ruling on a brother boycotting his brother, and the younger brother not respecting the older brother, and the older brother boycotting the rest of his siblings, knowing that both brothers are religious?

Allah has forbidden turning away from each other and abandonment among Muslims. The longer the abandonment, the greater the sin. Abandonment becomes a graver sin between brothers and sisters because it severs kinship ties (qata' rahim). Allah has commanded the maintenance of kinship ties and forbidden their severance, for "one who severs kinship ties will not enter Paradise." Each party should be forbearing and overlook shortcomings, choosing good words and excellent expressions, in compliance with His (the Almighty’s) saying: "And tell My servants to say that which is best. Indeed, Satan incites [discord] among them. Indeed, Satan is ever a clear enemy to man."