Query about the re-registration of property

Hi, My wife and her sister jointly purchased plot to sell it at better price. Since my wife was not able to attend registration and thought to sell it off asked her sister to register on her name. But paid registration expenses and cost. This was in 2006. But so far it was not sold and they do not have intention to sell. Since I asked we will register it so that we will also have authority on plot and they said ok. Now I need suggestion how to re-register the property on both without specifying boundaries that is both should have equal authority on property. It should be like both have authrity on half of the property and while selling both parties signatures required. It will great help if you could suggest how to register without further problems. Thanks