Seller cheating to repay the advance

We come to know that one property about 1000 sqt which includes empty land and very old house in it .it was in the name of a person called murugan.he mortgaged this property for rs 4lakhs in a private finance company. Later he died, he has two sons.actually murgan mortgaged this property to solve his elder son financial needs. So his elder son named Siva only paying this emi on monthly basis. But they are not paid it on every the bank agent comes and shout to pay the pending EmI. So finally both of murugan son decided to sell his property. Finally they approached a party to settle the amount in finance company, then they will register the property on buyers name. So party made a agreement for 3 months on a stamp a paper on the mortgaged property by receiving an advance of rs 50,000.later the buyer asked for legal heir certificate from the sellers.but they told that they don't have, because their mother died before his father and her death was unregistered.finally the seller assured that they will produce the legal heir certificate with in a month.but after 3 months also they didn't produced the legal heir certificate.whenever the buyer asks for legal heir certificate, they will simply say by next week it will saying this they have passed more than 6 months.meanwhile the finance company agent comes and shouts as usual and fine day he said that their company is going to auction this again the sellers convinced the buyer to settle their pending EMI in bank for rs 80,000. Initially the buyer refused to pay rs 80000 but the sellers convinced them and received rs 80,000. And they signed for this amount on the previous made sale agreement copy back side. But after 8 months also they have not produced the legal heir certificate.again they asked money from seller to pay rs 30000 EMI. The seller also given rs the total amount received from the seller is 160000. But after one month they received their legal heir certificate. So buyer asks the seller to settle the mortgage amount and to register on buyers name. The seller approached the finance company, to settle the amount.but finance company told them you have to pay 4.3 lakhs for closing. The sellers argued with the finance company for buying 4 lakhs , y should we pay still more than lakhs after 3 years .and they refused to settle.meanwhile the seller received one more 50000 from the buyer for their family financial needs. So this time the buyer decided to draft one more agreement for 3 months by including all those amount.and also did so .but after 3 months also they are not to settle the mortgage amount and register to buyer . Whenever buyer asks they simply says we made complaint in ombudsman. A letter will come later we will settle. Now totally one year over from first agreement and 3 months over from 2nd agreement.but they are not ready to settle finance as well return back advance to handle this? Buyer is in depression