Availing Loan on an unregistered property and subsequent registration

Dear Sir , I am planning to purchase a property in Maharashtra. The sequence of transactions is as given below : The developer sold a property to 1st buyer in the year 1988 . The 1st buyer got deceased in the year 1992. The legal heirs of the deceased person relinquished their rights in favour of their mother i,e the widow of the 1st buyer. The widow of the 1st buyer sold the flat to the 2nd holder in the year 1994. The stamp duty on both these transactions is paid alongwith the penalty in the year 2017 by the 2nd holder. My question to you is : 1) Since the stampy-duty alongwith the penalty is paid does one needs to get both these documents duly registered. How if the developer and the first buyer not available. 2) Will unregistered earlier sale deeds create any issues for me for availing housing loan. 3) Will unregistered earlier sale deeds create any issues for me while registering this property in my name . 4) Can my legal heirs have any issues in future by the governmental authorities Rgds Jay