Assalamo alaikum Respected Mufti saheb let me know that the brother in law is mahram or not in the life time of real sister who is in valid nikah with him and also let me know the list of persons who are mehram for a female and a male respectively.
Answer
(Fatwa: 832/589/L=1431)
According to Islam, the brother-in-law is non-mahram for his sister-in-law; it is wajib for sister-in-law to observe purdah with him. A mahram is one with whom nikah is haram forever i.e. brother, nephew, etc.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband