Sitting with non-mahrams in complete hijab

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.