If incase he has invested money in the same he has prove from where he has got that money...
Now as u hv stated above that he has sold some of his properties...Then when ever amount he has earned from that property will come under Long Term Capital Gain/Short Term Capital Gain on the profit amount he has earned on property @ 20% as per Income Tax Act.
To save tax hehas to invest money in buying a new house/building a new house on his own name.
However as mentioned above your grand father has bought the property on his own then and then sold the same to your father and your father has gifted the same to you.
Now if he has to file a claim on your property then he has to prove that he has invested money in the property and paid the amount to your GF/Father/to you.....
You can also visit to the contractor/builder who build your house and you can request him to issue the duplicate receipts for your purchase... or if incase any contract was done between both the parties (Contractor/Builder OR THE OWNER OF PROPERTY) then you can ask him to give you the photostate for the same.....