cancel power of attorney

Hi..I am manoj.I have 3elder married sisters and one younger brother. After fathers death; all of us with my mom are only nominee s of ancestral land property.My bro is a land developing agent ;he convinced us and made registered documents of power of attorney on his name telling reason's as AsI am a common serviceman in a private sector;I am always busy and he will develop land and construct a bungalow for us.Now after construction of abt 15 lakhs;he started selling the land property without giving any notice to me.I have sent a legal and a public notice to him to cancel the signed power of attorney. But invain. He is still taking meeting's with various parties for land deals and accepting advances from them. He is telling that he will sell only his. sisters and mothers share. But there is no legal disribution is done between us.there are total 60 gunthas.Kindly guide me how I can resist him from selling as I don't want to sell the same. What will be the share of my 3 sisters and my two sis are married before 1994.Pls give me ur kind advice. Waiting for ur reply.