Sitting with non-mahrams in complete hijab
Question

                Must a woman wear jilbab in the house in front of non-mahrams such as brother in laws or can she wear loose fitting clothes and head scarf?.
Praise be to Allah.What Allaah has enjoined on women is to 
    conceal their whole bodies from non-mahrams, including the face and hands. The clothing should be loose and not show the shape of any part of the 
    body, and it should not provoke desire. 
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah 
    have mercy on him) said: 
It is permissible for a woman to sit with her 
    husband’s brother or cousins etc., so long as she is wearing proper Islamic hijab, covering her face, hair and all of her body, because she is 
    ‘awrah and a source of temptation, and so long as there is nothing suspect about this sitting with them, and she is not sitting alone with any one 
    of them. 
With regard to sitting alone with one of 
    them, or in a suspicious manner, that is not permissible. 
It is more important that a woman should 
    observe hijab in front of her husband’s relatives such as his brothers, because the husband’s relatives can enter upon her and sit with her 
    without anyone denouncing that, then that may lead to regrettable consequences. See question no.
    12837. 
See Fataawa al-Mar’ah Jam’a al-Musnad, 
    p. 157.