I have grandmother's land. She died 25 years ago. Please advice me

My maternal grandmother and grandfather have 3 girl children.They have a house in Solapur. Youngest is my mother. 50 years ago my grand father died and 25 years ago my grand mother died. They havent made any will.12 years ago 1st sister of my mother died. my mother's 2nd sister is not married. She used to stay alone in my grandmother's house. Now that house is fallen due to rain. So my mother's 2nd sister is staying with us now in different city from solapur. Now since no one there in that house. My mother's 1st sisters son is building it again. He didnt even say that he is building that house neither to my mom nor to my mother's 2nd sister. When asked he is telling that he is building in only one part of the house. What should we do now. I feel they will some how grab that house from us. Religion: Hindu, Lingayat.