Can any of the Leagal heir's ask for their part of share...?

My mother-in-law was died when my wife was a 5year old kid, from then her grand-mother has brought up her, at the time of marriage her grand mother has gifted her a 2 acors of land which was registered as my wife purchased from her grand mother and grand father. Its two years now but the land was cultivating by my wife's uncle(her grand mothers son) with out paying anything to us and we came to know that he is going to question the registration in court as he is one of the leagal heir and did not signed on the registration documents. at the time of registration only my wife's grandmother and grand father has signed on the documents as they were selling it to my wife. Both grand mother and grand father are alive and they are only listening to their son and denying to handover the old pass books. we only have the registered document with us. Please suggest how can we get the old passbooks...?, as they are required for applying new one on my wife name, and procedure to take over the land from my wife's uncle..? As we want to sell it, can we do that with out any problems..? Does my wife will only be the sole owner of it...?