What is the validity for a registered and unregistered agreement?

Hi Sir / Madam, The question is we had purchased a flat in Bangalore from a developer through registered agreement but he committed suicide due to personal reasons and the construction was stopped in middle and it was completed just 50% and in meantime some other developer entered and agreed with all the flat buyers saying that he will return the money in the proportionate wise and everyone accepted and made a tripartite agreement between landlord, new developer and flat buyers to settle the agreed amount in 10months and he can sell the flat to others who are ready to buy the property as per his rate. For this we were not ready to agree hence we made a 200 rupees agreement with landlord and new developer saying they have to settle the amount within 5months but due to demonetization they requested for extra 2months time and they wrote a handwritten statement on the back of the new agreement saying they will return the money within Feb 28th 2017 but till now they have paid only 7lakhs and remaining 11 lakh rupees need to be paid to us. Now again they are asking for 1month time to settle the amount. Is it fine to wait till the time they have told without any other written agreement or do we need to anything else in between. Also i wanted to know what is the validity for a registered and unregistered agreement? example: A wants to pay money to B in 5months and incase they A wouldn't settle the amount to B in specified time, Till how many months / years we would be having power to file a case against landowner and new developer. Incase if we want to bring a stay order to stop the construction until our money is settled what is the court fee to be paid for a stay order in Bangalore civil court / high court.