Validity of an undervalued registration in sub-registrar office as per Limitation Act

Mr. X (Seller) executed a sale deed of Agricultural land in favour of Mr. Y (Buyer) in the year 1997 and the registration was on hold in sub registrar office for the reason being under valuation. The Ownership Khaata has moved in the name of Mr Y in 1999 (after 21 months potentially in a wrong way). Mr. Y’s wife Mr. Z gets the registration valid in the year 2007 by clearing the due tax payment as per the Property valuation. Mr. X and Mr Y has expired in the year 2002/2007 before the valid registration of sale deed been legally considered in the Registration office with out the signatures of heirs of Mr. X in Sub-registrar office. Though, the heirs of Mr. X claiming the property from the year 2008 from a civil suit with the WILL been registered 1978 in the Lower division court., I need your kind assistance on the below suspicions of wrong act with the incorrect process of sale deed registration - 1. Is there a lapse of time (almost 9 years) in making the undervalued registration to valid in sub registrar office in the above scenario? If yes, kindly assist me in providing the guidance under which relevant Act/Section we can file a WRIT Petition in High Court against the sub registrar office. 2. Can the undervalued sale deed registration made valid after 9 years post after the death of buyer and seller without the consent the legal heirs of seller (Mr X)? If No, kindly assist me in providing the guidance on the legal procedure of Mutuation of an undervalued sale deed registration for the period of 9 years after the expiry of Mr. X and Mr Y. 3. Since Mr. Y (Buyer) is not an Agriculturist to buy an Agricultural land., what are the mandatory legal documents a buyer should own before buying an Agricultural land in the year 1997 as per the Indian Constitution? Kindly help by providing the list of mandatory documents In the name of Buyer. This is required for legal heirs of Mr. X for claiming the property in the Civil suit.