How can we the sisters get the property???????

I am the eldest daughter of my parents among the 3 sisters and 2 brothers. actually my mother is the 2nd wife of my father, having a previous marriage with 2 daughters, who are married many years ego. my father had a property of almost 6 kathas. when he died, i and the younger sister and my elder brother were married, but the sister after me & the youngest brother were unmarried. then the property land was divided into three (3) parts each including almost 2 kathas and given to my mother, the elder and younger brother [we, the sisters, had given off our claims on property]. after that the elder brother started to live separately with his wife and two children in his own land. but recently my younger brother and my mother passed away in 2 different accidents. the 4 katha land belongs to them (2 kathas of each) is now in question. as one of my sister is unmarried, she is living alone in this property. the elder brother is now trying to take all of the land under his possession. but legally we, the sisters, are also successions of the property. he and his wife is torturing my unmarried sister for this both physically and mentally. then she was obliged to do a police diary. but now she is suffering a lot and nothing can do alone. so now what can we do????