What is the way to deal with the family's rejection of a young man who has become Sunni in a Shiite family, and the intense grief he experiences because of that?

Man is predisposed to grief due to people abandoning him, but the believer has been guided by Allah to the outcome of patience and forgiveness. The outcome of patience in the face of harm from relatives is praiseworthy. And whoever maintains ties of kinship despite their severance has truly fulfilled the meaning of maintaining kinship ties. What helps one endure with patience is emulating the Prophet Muhammad, peace and blessings be upon him, for he was harmed and forsaken, yet he persevered until Allah granted him victory. This abandonment by siblings might be a blessing, as it could spare the Muslim from their innovations (bid'ah). The Muslim must worship Allah with patience in such circumstances and respond to ill-treatment with kindness. One should also seek the company of religious and righteous people, and show kindness to one's mother.