Bought a property, seller ran away with Money

My parents who are senior citizens sold their prime home in north Delhi and bought condo. All proceedings happened simultaneously since they had no other cash . Selling their property went well. They bought the condo from a reputable investor and paid him 90% amount and took the date for property registration. Meanwhile seller agreed that my parents move into the condo which they did. Seller didn’t show up at the registration date , the day he was supposed to bring the original papers. Next day it was discovered that he did a fraud of mAny crores. My parents filed a complaint and submitted papers for FIR . Now bank showed up at the door saying that the condo belongs to them and the loan was given to the seller. Some lawyers are asking us to approach bank for settlement and others are asking to wait for a notice and yet some said that they have a right to get the property vacated! There have been many opinions. My parents have always lived an honest life Nd they are being pushed in different corners . Can someone tell us the usual process in these cases. Is there any hope? What all shall we keep in mind going forward? Thank you.