Respected sir,my father has two wives.He after the oral consent of first wife which is my step mothe

Respected sir,my father has two wives.He after the oral consent of first wife which is my step mother married to my mother, my mother died on may 1,2019,she had a house and a agriculture land. My mother has two children me and my married sister. My step mother has one son. Plz tell me who is my mother's legal heir. Further when we apply for legal heir certificate village lekhpal(patwari) has rejected our application saying that produce divorce certificate for first marriage. What should we do now plz guide.