Got notice of cheque bounce

Dear Sir, I am a software engineer.My parents took some amount of money from one party and in return they gave them blank check with signature for guarantee purpose. As My parents were in continuous need of money so they provided multiple check to the same party. and 3 month back when other party asked them for money , My parents told them that they will sell their house and return the amount, In that case those people took sign on house property papers and Shop papers with an amount of 20 lakhs and 10 lakhs respectively, that if my parents are unable to pay money till september 2015 then they are liable to claim both house and shop. the actual amount which is taken by my parents as a whole is around 2.5 lakh which with interest would be around 4 lakhs max. But now they are asking my parents to give them house legally and when my parents denied it they fill one of cheque with amount 1.9 lakh and submitted it to bank and that cheque got bounce as their was no sufficient balance in that account. They sent a legal notice for cheque bounce under section 138. My parents are ready to pay them 4 lakhs Rs. including interest which they borrowed from other party but they are now saying that you took 30 Lakh Rs. so either you pay us whole money or legally sign the house on our name. My parents are also trying to sell their property so that they can return back the money which they actually took from them(4 lakh to be precise) but they are saying that they will take stay from court as they have papers with them according to which my parents are liable to give them house if they are unable to make payment till September 2015 . Can you please suggest me some way how we can come out of this fraud. It would be really a great help.