Cash Handed Over To The Concern Party But The Party Is Denying The Same.

This case is really important to me and my family. My father is undergoing major depression therapy because of this. Any help would be really appreciated. Background: My father and his sister's husband bought two pieces of land that are next to each other. My aunt's family husband died in the 90's and they are poverty stricken even before. My father had been supporting them financially forever. Now, my aunt's family sold if land in-return for money during their daughter's wedding. They handed over the land documents as consent but my father failed to register the land under his name thinking that there won't be a need for it (all emotional sister stuff). And the document is still under their name. we do not have a proof for the money transfer But now their entire family had turned up against my father, demanding the piece of land. Is there anything we can do just with the land documents.