Partition Deed Lost

My father in-law has a property inherited from his parents. After both of the parents have passed away the property was divided between himself and his only brother. Property deed was registered and the original copy was in the possession of my father in law who was the eldest son. Later, for some reasons his brother took this original deed from him though the later had a copy with him already. Both parties later had a dispute on some other matter and they are not in good terms. When mu father in law asked his brother to return the Original deed took away from him he denied. In the mean time we heard a rumor that his brother is going to sell my in law's share to someone else. My in law got worried and managed to secure a duplicate of the previously registered deed from registrar's office. Still he is worried about the matter that the original deed is not with him. Is there anything to be worried on this matter? Please help us with your valuable advise. We belong to Keralite Christian family.