Disinherited

We are from assam where my father had two flats. One flat was given to my married sister when the mental faculties of my father was ok. Now when my father attained and age of 92 years my step brother who live in chandigarh came over to Guwahati and called a family meeting wherein he promised to take care of the financial needs of my father out of the sale proceeds of the remaining flat and the balance he would give it to wife whenever I get married. I replied that I am not going marry and want the flat to live. To this he gave a vague reply and hurriedly went out of the house. I presume a will has been made transferring the property to my step brother. My father was not in the condition to write a will, hence I doubt that the will was drafted by some professional where my father only signed. All this happened in 2012 and my father died in august 2015. My step brother being the beneficiary and the executioner himself died in January 2016. No probate has been taken till date and my sister in law and her sons locked up the place and want to sell it off and bring all the money to chandigarh leaving me nothing. Please help me to get my Share and also please advise me as to what law has for me. .