Question: I am married to a woman who wears hijab, praise to Allaah, However, as is the custom in my country, she does not wear hijab in front of her sister's husband and her sister does not wear hijab in my presence. This is the custom. Furthermore, my wife does not wear hijab in the presence of my brother or her cousins. Does this go against the Sharee'ah and religion? What can I do while it has become the custom in my country not to wear hijab in the presence of those people that I mentioned. If I tell my wife to wear hijab in front of those people, she will accuse me of not trusting her and being suspicious about her and so forth.

Response: All of those groups of men that you mentioned in the question are not mahram for her. It is not allowed for her to uncover her face and beauty in front of them. Allaah has only allowed her to uncover in front of the mahram men mentioned in the verse in surah al-Noor, "[Tell the believing women] not to reveal their adornments except to their husbands, their fathers ......" (al-Noor 31).
First, you should convince your wife that it is forbidden to uncover her face in front of non-mahram men. Make her abide by that even if it goes against the customs of your people and even if she makes accusations against you. You should also make this point clear to your close relatives that you mentioned, that is, the brethren of the husband, the husband of the sister, the cousins and so forth. All of them are non-mahram and they all may marry her if she gets divorced. ("Islamic Fatwas regarding Women")