Will the father be sinful for boycotting his sister for two years, and will the mother be sinful for considering her brother as dead due to his boycott of her?

The status of kinship ties is great, and a severe warning has been issued against those who sever them. Allah Almighty says: "So would you perhaps, if you assumed authority, cause corruption in the land and sever your ties of kinship? Those are the ones that Allah has cursed, so He made them deaf and blinded their vision." And the Prophet, peace and blessings be upon him, said: "A severer of kinship ties will not enter Paradise." Therefore, a person who severs kinship ties must fear Allah and dread this warning. And whoever repents, Allah will accept his repentance. Maintaining kinship ties can be achieved by any means, such as communication. It is appropriate to advise the one who severs kinship ties and to involve righteous people for reconciliation.