1. If the agreement for sale between previous owner and these 3 people is not stamped and registered, then these 3 people do not have a clear title to the property
2. the Will and GPA which they hold is of no use and those do not confer any title on them
3. the Supreme Court has said that such transactions using Will and GPA are done to evade payment of stamp duty on property transfers, therefore they are not valid
4. I would advise not to proceed with the deal
5. just for curiosity ask these 3 persons whether the lady from whom they claim to have purchased this property, is agreeable to sign the sale deed with you as a confirming party - i am certain that they will not have any reply to this. Even if they have, please insist for a registered document between the lady and these 3 people
6. this is the precise reason why no banks are ready to give loan for this purchase