Dear Friend,
DO NOT SELL ON INSTALLMENTS - lets have a small example : you are selling your car and transferring the ownership as well without taking full amount of the car because the buyer has said he will check the car for 15 days and will pay the money .
IN YOUR PROPERTY SELLING case once you have done the registered sale deed the buyer will not pay you the money and you will end up running around in courts - once the sale deed is done and the property is transferred the COURT AS WELL will ask you the authenticity of the sale deed and at that time you will not be able to explain the term of sale.....
Hence it is suggested to take all the money of the property before selling or dont sell it all together -
ALTERNATIVELY - you yourself apply for N/A post that sell to the concerned party - and they should agree to this -
You can take some money and do a registered AGREEMENT TO SELL and take some 20-30% and as a precondition to sale deed mention in the agreement that you will get the N/A done and in case NA is not received you will return the money.