Property partition between christian sisters and brothers

My grandfather (mother's father) had died without leaving a will in 1983. The land is divided into a family bungalow (where my uncle and his family live) and a smaller bungalow that was leased out to my mother in 1975 to build her own bungalow on. Her other sister is also a leasee being given a room in the family bungalow to live with her husband for a few years. On the day of their respective marriages, my mother and my father and her younger sister and her husband were made to sign agreements to accept cash of Rs 5000 and jewellery (basically their wedding jewellery) and not claim ownership to the property. My uncle (mother's brother) put her in court in 1984 to claim sole ownership on the bungalow stating that she and her sister had signed these agreements and have lease agreements and are therefore not owners. The third sister married a hindu and does not want a share. Under christian law and the Indian Succession Act 1925, aren't brothers and sisters entitled to equal share if their father has died intestate? Also is there any claim to them signing these agreements at marriage and having lease agreements, valid for them not receiving a share?