How family property is shared when father has two marriages ?

My father had two marriages. I am the only son from my father's first marriage. My father had self acquired land ( 8500 sq. ft. ) which was purchased by him long ago when my mother was alive. After the death of my mother, my father married again and with his second marriage, I have one step brother and one step sister. He had purchased another land of 8500 sq. ft. later on. So, his total 17000 sq. ft. land is now inherited by us. My father and step mother both died and did not do any will. The property had two names, me and my step brother. My step sister's name was not on the property as per our society tradition. But lately, my step sister is demanding her share in the property and she went ahead and got her name added in the property. So, the property has three names now. My questions are : Do I get half the share of all property or one third share. ? Is it possible that I get all of 8500 sq. ft. land acquired first by my father plus one third share in another 8500 sq. ft. land acquired later ? Please help me with expert advice. Thank you very much.