Want to know my right on my parents property.

Hi, My mother was second wife of my father. He married my mother without giving divorce to his first wife. He has two children from his marriages, 1. Son (from 1st wife) 2. Daughter / Me (from 2nd wife) ** Both wifes are not alive. He married my mom secretly in a temple and started residing with her only. My mom bought a land in the name of my father and later on they build a house on the same land. House documents are on the name of my father but 90% of the expense was paid by my mother to purchase and build the house. In the year 2011 she got died as she was suffering from Cancer. Now my Step brother (son from 1st wife) trying to accuire our property by convincing my father. And he is also quite convinced because he like his son over his daughter as his son can grow the family branches further and a daughter cannot. His Son (my so called step brother) has 4 children - 1 son (married with 1 kid) , 3 daughters. On the other side - From the past 9 years I am living all alone in a different city. I left home for higher studies and then for job. And my present status is - jobless and running short of money. Now my father is asking me for the property papers which my mom handed me before leaving this world. Kindly guide me what step should I take to stop the people who are making plans to accuire the property.