Dispute between Mother and son regarding Land ??

Religion HINDU Assam In 1953 A LAND property was purchased by My grandfather and his brother in the name of my grandmother who was just 13 yrs old being a housewife...In 2004 my grandmother with the help of my uncle filed a suit in court against my father that SHE IS THE TRUE OWNER OF THE LAND, providing theJamabandi copy of Chitha Mutation which was in her name and her own witness that she purchased the land at Rs.90 being it as her stridhan...But in 1963 1/3rd part of land was mutated in the name of my Grandfather's brother who is an extra party on our side as his right in the land....Now question is Whether she is the True owner of the property or not ?? As she said, she purchased it with her own income, then What is her source of income ?? Moreover If the land was purchased by her stridhan, then why my Grandfather's brother acquired 1/3rd of land mutated in her name as his right and part in the land...It must surely a Hindu Joint family property...Help me if these pts are correct