Cancellation of validity expired registered sales agreement.

My father entered into an agreement with a seller for purchasing 3.5 cent residential land in 2014 and the sale agreement was registered in sub register office upon payment of Rs.1 Lakh as token advance and balance amount 4 lakhs to be settled at the time of transfer of tile within a period of one year from the date of sales agreement or buyer to loss the advance payment. Due to unexpected circumstance, the seller couldn't come forward to register the land in my father name within the time frame and sale agreement time also got lapsed. The seller of land is well known person to my father hence both parties not bothered about time lapsed agreement and did not extend or cancel the sales agreement mutually. The buyer of land, my father expired in 2016 and the seller approached my mother in 2018 to cancel the sales agreement as we want to sell the property to a new buyer for his urgent financial needs. We are three as legal heir to him, two brothers and mother. When i approached my brother for cancellation of sales agreement at sub register office but he refused to come forward to sign for cancellation of sales agreement due to dispute he had in sharing the property and claiming extra share to performing his duty. The seller who had return the advance payment Rs.1 Lakh in our presence to purchaser (My Father) in 2017 but he failed to cancel the agreement as we was relocated to another state for his profession. Now the seller is in trouble to sell the land to new party as the sales agreement entered with my father is reflecting in encumbrance certificate. In this regard, we have checked with many lawyers for getting legal opinion on this case but the opinion was differing person to person. Hence i would like to have an experts advise through this plat form e and would appreciate your value feedback on following points. 1) Even after expire of registered sales agreement whether it should be cancelled at sub register office? 2) If yes, please advise the procedure to cancel the registered sales agreement since one of the legal heir is not ready to cancel the agreement because of dispute related to family matter. 3) It is the responsibility of legal heirs to resolve the issues if any left by deceased person before claiming for his property. In that case whether the legal heir who is not ready to perform his duty to resolve the issues left by deceased person, will he eligible to claim property under the law? 4) The seller filed a cases in court for cancellation of expired sales agreement and court summon was served to me and my mother but the court summon sent to my bother address who lives in different state got returned as he changed his resident recently. The case is at court more than year pending for judgement.