Notary agreement is valid or not

You can contact the legal heirs of the deceased to perform their part of contract on the basis of sale agreement or to return consideration amount received 

Notarized agreement for sell is valifand can be enforced but you have to pay stamp duty and registration charges.

You can file for suit for specific performance against the legal heirs of property if they refused to execute the sale deed. Since the property owner has already sold the property against sale consideration.

You have to pay duty penalty for unregistered document issue legal notice to heirs or approch personally if they refuse demand for money with interest and compromise.