Answer
(Fatwa: 1315/1034=H/1430)
Mahram is one with whom marriage is haram and unlawfulm forever, like father, uncle, real brother etc.
(2) The parts of body which should necessarily be covered before others are satr.
(3) If there is no fear of fitnah and lust, she can keep her face, head, hands and feet uncovered before her mahram members. Covering the other parts before mahram is also wajib (necessary). The transparent and tight dresses which reflect the body colour and structure especially chest and which are worn commonly by women are unlawful to be worn before mahram as well; since such wearing dress is like keeping oneself without dress (except before husband).
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband