I presume that the legal notice is sent by your eldest uncle to your father 'to register the open plot' in his name. In your own narration, you have stated that the eldest took the open plot and the same is written in the affidavit signed by three brothers. I fail to understand how can corporation register 'half house' +'open plot' in your father's name. Your eldest uncle is only just in claiming his share of the property. However, the correct opinion can be given only after perusing the papers. How did your father & his brothers got the right to divide the house and the open plot amongst themselves. Was/were there any other sibling/s?. Did your grand father died intestate(without leaving a WILL)?. Is there a WILL of your grand father? You also say that "No registration was done", in that case, they would not have paid stamp duty to the govt. Then the document would not be valid. Better to consult a local Advocate with the documents to proceed further.