According to ecclesiastical law, a widower could not marry his wifes sister and a widow could not marry her husbands brother as these marriages were within the prohibited degrees.

Is it legal to marry your wifes sister?

Marriage with a deceased wifes sister is to be legalized, but not with a deceased husbands brother; with a deceased wifes sister, but not with a more distant relation, a wifes niece.

Can a man in New York marry his widows sister?

Originally Answered: Is it legal for a man to marry his widows sister? If a man has a widow, hes dead and cant marry anyone. If you mean a man is a widower (his wife has died) is it legal for him to marry one of his wifes sisters, then it is legal for him to marry his former sister in law in the United States.