TDS on NRI Couple selling property to Resident buyer

Property owned by NRI couple Purchased as a semi-finished house in 2010 Sept. for 30 lac, paid 2.2 lac for registration and 4.4 lac for additional construction. owner spent additional 10 lac money to finish the building but all the work was done over period of one year (2010-2011). most of finishing work done by local small time construction workers and paid through cash. Now the same property is being sold to a resident indian for 67 lac. planning to register in march 2017. Need to obtain TDS estimation for long term capital gains. who calculates the TDS estimation? is it buyer or seller or a CA? I could not find any clear instruction document as to who prepares the estimate for the buyer to deduct TDS. For NRI couple, is there any way to completely avoid TDS under double taxation treaty. couple lives in USA. no plan on re-investing the money in any property for now as the real estate sales frozen due to demonetization. Thanks in advance, looking forward to getting your valuable advice.