Two properties bought next to each other

My Grandfather who was former Additional District & Sessions Judge bought two properties, one of 3000 sq.ft. and other of 1800 sq.ft. in the name of my Father in 1991. However, only one 3000 sq.ft. was registered which has been sold by us 2011 and for the 1800 sq.ft plot, full payment was made but only agreement, affidavit were made as my Father had to leave for occupation outside of India. When he returned back in 1996, it was notified to him about Ceiling & Regulations Act and that on one party two properties cannot be registered. Thus, this property still remains as it is. The original seller has left the State & died. My Father too died. Now, how to proceed for sale. I have few party with me right now? Is Sale deed required to sell? As per Islamic Law it comes under debt as money was received by my Grandfather for which I have letters of him but only agreement was made so the land equal to that proportion has to be returned. So should I demand my portion of 1800 sq ft share from his estate? Or, should I make Trust Deed? I have heard there is something called as Land patent as well? Kindly tell all the options available with me right now? Thanks & Regards