If your brother is withholding property documents and delaying the mutation process after your father's death, you have several options. You can issue a legal notice demanding partition of the property as per your father's will. If this is ignored, you may need to file a partition suit in court. While mutation is the official transfer of ownership in revenue records, it doesn't affect your existing title. You can also explore applying directly to the revenue officer with the death certificate to initiate the mutation process for both your names.