What should a son do about his mother who has shunned him for preventing his brother from entering a house that has become his property, after the mother had supported the brother in his endeavor to seize the house and expel the son from it? And is the son sinful because of this shunning?

Your brother made a mistake, but do not cut ties with him, for maintaining kinship ties is obligatory, even with one who wrongs you. Obey your mother regarding your brother's entry into your house, unless you incur significant harm, for honoring and obeying one's mother is among the most incumbent duties, and disobeying her is among the grave sins.