Protect my Mother

Dear sir/Madam I am seeking for legal advice to protect my mother. My mother has a threat to her life with our second elder sister. we are total four kids to our parents.Two elder sisters,me and my younger brother. both of my sisters were married and second elder sister family has disturbed . she separated from husband and living together with someone . None of our family members did not know the complete details with whom she is living. She had two daughters among them elder daughter is living with us from child hood but younger daughter is always saying with her. When ever she need money frequently visiting to my house and threating to my mother beating her very brutally ,harassing her and taking away all valuable items like Gold,Silver etc from my mother and my younger brother along with my daughter in law all are staying one small house . My mother and brother bother are uneducated people and they are very innocents ,My self is living in other country due to my job and i am not in a posiition to visit India frequently I am taking complete responsibility to my daughter-in-law education expenses and my family is sustains with family pension. my father was expired in 2011 we have small property . we are happy to share the property equally among with all others .Please suggest me how can i prevent my sisters harrasment and protect my mother. Thanks Sairam