Jointly Owned Independent House-Need Help

Hello All, I have a jointly co-owned independent house in Bengaluru with my younger brother on a 50-50 ownership each as per sale deed. It is a duplex house with no seperate stairs from outside and a common entrance up until terrace. It has no seperate floors split and built into G+1 floor and a terrace. Now my brother has picked dispute to either sell my portion of house share to him but I have no interest in selling the house at all. Now after discussions we have decided to sell the house entirely to third party and seperate. But he has undervalued the house via independent valuator for which I have not agreed. I have decided to retain my portion of property and build a new house instead. My question is, since this is an independent house how can bifurcation happen and seperate ownership possible? Secondly, should we execute partition deed in sub registrar office and is it valid for such a house? Can I approach BDA for bifurcation of land though there is a house built on it? How can this be settled please guide me. Regards, Ravi SP