We Want To Be Real 'sister' Wives

My sister accuses our 'husband' of looking for a cult. Why? Because he likes living with and having sex with me and my sister. In the Bible men can have two wives, why not two sisters? We are eighteen months apart, from babyhood until we left home we shared a room, now we share a room, but we also share a husband. He doesn't preach religion, he just wants us married to him together and he is looking for a religion that will marry us. He is not looking for a cult. Why not move where we aren't explaining our life to everyone.