Contact Advocate first and get confirmation as to wife has sufficient inccome and after death of her husband she has repaid the loan out of her personal income. As far as I know, it is in order to return the title deeds to any one of the joint parties, it is not Bank's duty to locate correct heirs and deliver the title deeds to them. This is great injustice. Even in case of joint accounts, if one party expires, bank simply obtains a death certificate and pays the amount to other. Succession rules are not for Banks/insurance companies . This is the very purpose nomination is introduced to prevent harassment by Banks/ insurance companies.. Mere handing over title deeds can never create exclusive ownership.
There are several precedents in courts. Help her in finding such earlier judgments against banks insisting such idiotic, self invented rules to harass innocent and help less widows. First issue notice and get all documents obtained from the borrower, there must be some clause that states on such return of documents.
Also search in google and find out the obligations on discharge by lender in Joint borrowal accounts.
Also keep correct caption for query to avoid confusion. Bank is different from Housing finance company.