A husband as a non-Mahram to his sister-in-law

Q 1: I have two unmarried sisters and two who are married and have children. The problem is that my unmarried sisters do not veil their faces in the presence of their sisters' husbands, When I told them that this is impermissible, they said that our father did not forbid that before his death and that I should do the same. I do not know what to do, knowing that I supported my opinion with texts from the Qur'an that this is Haram (prohibited) and impermissible. Kindly give me your Fatwa (legal opinion issued by a qualified Muslim scholar) in this matter. May Allah reward you best.

A: It is not permissible for a woman to unveil her face in the presence of her sister's husband, because he is a non-Mahram (an unmarriageable relative) to her. It is known that if customs contradict the Shar`y (Islamically lawful) ruling, they should be abandoned and the legal ruling should be adopted. You did well in rejecting their behavior; may Allah bless you. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.