Wrong registration without mutation

Husband has a 1 acer of agriculture land bearing survey number of 217/1G He transferred it to his wife with same survey number with out mutation. After husbands death the family members changed the passbook from the name of husband to his wife by producing the death and leagal haire certificates,and it got changed. After 14 years there came a party saying that this property was sold by his wife. That sale was done without the family members knowledge, In that sale document and EC it is mentioned 217/G as survey number, The buyer who came does not have any mutation/ pattadar paasbook for that bought property until 14 years. Now they approached MRO claiming that they bought this property and we need mutation or passbook but MRO refused to do, As of now all the information about the ownership in online and passbook, proper taxes are in her name. She is alone now two children and husband are died. Her husband elder brother daughter as looking after this property issue. What can they do to save this property from the fraudulent please suggest.