Are legal heir of dead fraud builder responsible for returning the money?

I bought an apartment (under development) in Karjat Maharashtra in 2011 and the builder was a fruad. Many complaints were filed against him and he was caught in 2019 but sadly died in custody during pandemic. The builder was operating along with his wife and she also died of cancer. This builder couple have duped many home buyers and have many projects under their company name in Karjat, Pune and Alibaug. The land on which the project was being built has been taken over by bank and they have sealed the area. My question: 1. What should be the course of action for a buyer who has paid stamp duty and registration fees. Is there a way to get it refund because clearly the property is nowhere now. 2. Legal heirs of the builder couple have come out of thin air in 2024 and claiming the rights to the assets (other completed projects where society is formed). But in cases of fraud/loss like our project they are saying they are not liable. Are they not legally bound as legal heirs to pay our money? 3. Can bank sell the land without informing the buyers? 4. What should be the future course of action? Thank you