Purchasing house from father

My family and I live with my parents. I recently approached my father about buying the house we live in from him. When we approached my brother about this matter,he refused as he said I was offering too little for the house. Am I depriving him of his rightful share?Do we need his permission to conclude this transaction? Can my father & I conclude this transaction on our own,without his permission? We approached him as we felt that we did not want to do anything behind his back, however this has now created animosity between him and us.
Please advise if this is correct in terms if the shariah, (me purchasing the house at a lower amount agreed to between my dad & me). Jazakallah