Law to take care of old widow mother and mentally challenged unmarried sister

Recently my father died leaving my 74 years old mother and 50 years mentally challenged sister. We are three sons . Elder brother hs been engaged in govt job against my father's job on rehabilitation. I my self an employee in a private engineering school which is not running since 2018 due to management dispute. My younger brother is shopkeeper and earn from father's cultivated land and casew field. My fa#ther was a govt servant and pension holder. Since last 30 years I was taking cre of my parents and sister. But now after my father's death I became helpless to find the way for proper care of my widow mother and mentally challenged sister as my brothers are in that mentality to take parental property share as well as my mother's family pension without taking care of my mother and mentally challenged sister. My brothers didn't even agree to give a single pie for father's Shraddha after his death. I shall be highly obliged if the law for taking care of my mother and mentally challenged sister as well as proper sharing of parental property with proper responsibility towards my widow mother and mentally challenged sister.