What is the ruling on sleeping over at one's sister's husband's house in the presence of a mahram (such as the mother or husband), knowing that the sister's husband and his sisters are religious people?

It is permissible for a woman to sleep in the same house with a man who is a stranger to her if the house is spacious enough for each of them to have a separate place where the other cannot see their 'awrah. However, if the place is cramped, it is not permissible except out of necessity or extreme need, while ensuring that the 'awrah is not exposed.