Is it permissible to remove the hijab (head covering) in front of one's sister's husband if everyone lives in the same house and it is difficult to maintain it constantly?

It is forbidden for a woman to uncover her hair in front of her sister's husband because he is a non-mahram, and her hair is considered 'awrah by scholarly consensus. There should be no leniency in this matter under the pretext of cohabitation in housing, as such cohabitation is impermissible and leads to unlawful seclusion (khalwa). The Prophet, peace and blessings be upon him, warned against "al-hamw" (the husband's relatives who are non-mahram to his wife, such as his brother) and described them as "death."