Defending a false suite

sir my naani (grandmother) Was never married and was the only daughter, she lived with my naana g (grandfather) and given birth to my mother and my mother was also her only daughter my naani died in 2004 so the property was inherited by my mother. Although there is her unregistered will also but at that time the revenue official said that it is not required as she can inherite the property as a legal heir. Now in 2015 a person who is our relative filled a civil suite on us saying that my grandmother was unmarried and issue less that person was having his name in Jamabandi but before 1996 as he and Nani transferred the lands he left his land in our village and naani left her land in their village there are proper mutations for this act Sir plz suggest me how can I defend this case as we have been referred strangers to our property by him in this case although we are the owners in possession as well as in the documents. That person has not even a inch of land on his name in our village. Plz guide me