Property fraud

I bought an agricultural land which is in name of person who is dead. I bought from his successors i.e. his mother, brother and sisters (as he is unmarried). The registry has also been done a year ago. Now for mutation, patwari said we have to file the mutation of succesors of dead owner first, then mutation for sale deed will be filed. For this, those person are not giving the documents to patwari and getting mutation and now demanding more money and saying otherwise we will sell again the agricultural land to other person with higher rate. Please provide legal suggestion. What to do?