nanaji means - mother's father.
property was bought in your elder brother's name (and he probably being a minor your father being a guardian in the transaction)
property was bought using your mother's father's money.
Q is: did your mother's father gift that money to your mother or your father or your elder brother?
firstly , it is not a benami property.
your don't seem to have any claim. apparently.
but do take a second opinion.