CHAIN OF TITLE DEED.

Hi, this question us about our property. We have a 1bhk in thane, maharashtra. We bought it 20 years ago. We are the third owner of the house. Now we want to sell the house but we are facing a document problem. The buyer of my house wants the agreement done between the builder and the first party. This might have taken place at least 40 years from now and we really don't know whether the first buyer is alive or where he is located etc. With us we have the copies and original done between 1st owner to second owner & second owner to us. We only have the Xerox copy of the agreement done between builder and 1st owner and we do not have original. This is the problem due to which the sale is not proceeding ahead. Please let me know what to do to come out of this situation. ? 2nd question.................... How to find if the property has been Registered by the second owner after he bought from 1st owner. How and where to look for the same in the agreement as we cannot find it? After we have purchased the property from second owner we have not done registration and the same has been told to buyer. Pls guide me on how to do the same. Also the buyer is opting for loan and for this only thing which is pending is buyer wants to know if the second owner has registered the property after he bought it so that he can get the loan. I know that my query is a long query and a complicated one but I need to dispose my flat at the earliest to fund my mother's medical treatment. Please help me.........................