Property Transfer Ownership of my mother’s Property: Legal Procedure & POA for Selling

It is regarding Property Transfer Ownership of Chennai Plot: Legal Procedure & Power of Attorney for Selling. My mother died 20 years back and she has a property in Chennai. My father is living and married another woman. We are two brothers. My father is trying to sell that property which on my mother's name. 

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• Poa violation in joint developer agreement
• My father is looking to add my mother's name to a home

Does he need our signatures to sell the property? Does he need our signatures to convert the property on this name? Is it possible to sell the property directly to buyer by providing my father and brother's signatures. What is the tax rate on land sale in Chennai during Property Transfer Ownership process? Kindly suggest.