1) on your mother demise intestate you would have one third share in said land
2) your father and sister can execute gift deed or relinquishment in your favour .
3) gift deed/ relinquishment deed in favour of close family relatives attracts nominal stamp duty
4) apply for mutation of land in your favour . enclose mother death certificate , gift deed executed by your father and sister
5) if your mother had executed will in your favour apply for mutation and enclose will made by your mother . notice would be issued to your father and sister . if no objection received land would be mutated in your name