What legal rights do we have for property resolution?

Hello, I am seeking assistance on a matter that includes my father's house. My father passed away 2 years ago without any will. My mother and I signed a contract to a local contractor to make a flat out of my father's house but my sister who was adopted by my father is denying to sign the contract without any reason. My sister is from my mother's first marriage (her 1st husband was dead) and was adopted by my biological father in 80s. I am an NRI and it is difficult for me to resolve the issue by coming to India many times. Is there any legal right for me and my mother to resolve the issue so that the work can start in my house? I do not want to deprive my sister of any earthly possessions that my father left I just want the issue to be resolved so that my mom can be in peace in her own house. My sister is married (2nd marriage) and has a son (from her first marriage). Thank you.