Hi
The answers are as follows:
1) An unregistered agreement to sell cannot be admitted as evidence as Section 17, 49 and 53A of transfer of property act will come in to play and courts cannot admit the document as evidence.
2) However, an unregistered agreement to sell, can be used to invoke relief under specific relief act, but hereagain the Seller has taken all steps mandated in law to cancel the agreement . Therefore the very fact that
a) Seller had issued legal notices (which were returned unserved) and
b) Seller issuing paper publication in news paper
means that the seller has taken all steps to rescind/cancel the agreement and as such the Seller is under NO LEGAL OBLIGATION to execute the sale deed.
3) Given that much time has elapsed (i.e 22 months from date of agreement to sell) and buyer has not come forward to perform his part of contract, the 2 surviving sons of the seller can proceed to sell the property to a new buyer without any further notices to previous buyer.
4) Courts will not grant order in favour of previous buyer even if the previous buyer approaches the court for relief under specific relief act as buyer has miserably failed to perform his part of contract despite passage of 22 months.
5) In law, even unserved postal notices are valid and added to the fact that paper publication has also been issued cancelling the agreement.
6)Refund policy- The seller may retain upto 75% of payment received and may return up to 25% of the money paid by buyer, provided the buyer approaches the seller. Third parties cannot make any claim to the seller as they are not parties to the contract(agreement to sell dated [deleted] and doctrine of privity of contract will strictly prohibit the third parties to make any claims against the seller.
Hope this information is useful.