Release deed by my brother

I am Smt. K. Vijaya from Chenai. We are three children for my mother. My mother has passed away on the 5th January 2020. A house property in the name of my mother, measuring 467 sq. ft. with a house, has been registered by a settlement deed in favour of all the three children, in October 2017, by my mother by way of a settlement deed. The settlement was done with consciousness of my mother out of her free will. The eldest is sister aged 72, the second is my elder brother aged 71 and myself aged 65 are the legal heirs for the property. After registering the settlement deed in 2017 by mother the encumbrance certificate shows the names of all the three legal heirs. My brother is a divorcee and mentally deranged. We want to sell the property and share the proceeds among all the three of us equally. The purchaser has been identified. My brother is not cooperating in executing the sale in favour of the prospective purchaser. What shall we do to overcome this problem? We have agreed for a higher demand also made by him. In the circumstances, whether we can go in for a release deed / settlement deed by him in our favour specifically mentiioning the amount payable to him and register the property by both the sisters in favour of the purchaser. My email id is [deleted].