Co partitioner has stolen the property papers and sold his part

My grandfather owned a room in one of the main area of park street under the pagadi system(tenancy model). After his demise the room belong to his 2 sons, My father and my uncle. My uncle and his family were residing there and they didn't want us to interfere in such property. But somehow me and my mother were able to tackle the issue made a partition of the property with plywood. My uncle and ant had stolen the property document from grandmothers box when she was alive. And Now they sold there share of the property without our consent to a third party and also handed the entire property document to them. We only have the part of room with plywood partition. We don't have the papers and also the person who bought the property do not want the partition with brick walls and want us to sell our share of such room as per his value by unwanted pressure. We can't rent or sell the property without legal papers and proper partition. I want to what are the legal remedy remedies available to us to get the papers, and partition the property.