How to start selling a registered agricultural land that has been blocked by registarar.

Hi, We have a ancestral agri land in tamilnadu which was purchased by father's grandfather. My father's father died in 1974. My father got his share of agri land in 2013 as a settlement deed from his elder brother, got registered and have patta also, and now we wanted to sell it, but my father's younger sister who got married in 1973 has filed a petition in registarar office to stop the sale of the land. We have all documents pertaining to the above. Now, it has been blocked by providing wrong info to court that this land belongs to my grandmother and it was gifted by her just to buy time and enjoy the land cultivating. Now, what is the procedure to unblock the land from registarar's office so that we can sell it? HOw long will it take?. We have contacted a lawyer and just replied to the petition notice and taking his own time and not informing us exactly how long it will take. We wanted to change the lawyer too. what is the procedure for that? Thank you Regards G. Gandhi