Son not given share in father's money is claiming all of it what to do

My father in law death on 26th Jan 2017 due to cancer and he has 2 daughters and one son. My wife is elder sister in both. One daughter and son is unmarried but my father in law not believe in son bcz he is not carrying his family and he is not in good line. So father in law appoint nominee approx all saving accounts and FD to my Sister in law. After death my brother in law attend and do all physically death ceremony due to Hindu religion. We decided give him approx 50 % sharing of father in law money bcz 50% for her marriage or her future. But my brother in law blame me and and his both sister we cheated him and he will go court against me and both. He is trying to harsh me bcz i support her. While we go against father in law decision and try to give 50% money bcz he is son. But he trying to take 100% money. So pls guide me how I protecte my self and sister in law before he will go court.