What is the reward for reconciliation with and forgiveness of an offender, given my brother's refusal to reconcile with my brother-in-law, who wronged him, and his repeated threats to kill him?

A Muslim may be afflicted by a passing thought from Satan, but if he remembers, he will recall and return and repent, as stated in the Almighty's saying: "Indeed, those who fear Allah - when an impulse touches them from Satan, they remember [Him] and at once they have insight." The better of two estranged individuals is the one who initiates the greeting of peace, based on the Prophet's (peace and blessings be upon him) saying: "It is not lawful for a Muslim to forsake his brother for more than three nights. They meet, and this one turns away, and that one turns away. The better of the two is the one who initiates the greeting of peace." It is not permissible to harm the brother-in-law or cause him distress merely through abuse and insults, let alone killing, which is one of the gravest major sins.