Bankrupcy Laws in Montana regarding mineral rights

My mother and father went through bankrupcy court about 7 years ago and they were told that they lost their mineral rights and a company named Choctaw Energy bought them. They were not aware of this until the day of bankrupcy. I have been trying to research this as oil is moving into our area. I was told by a landman that this was not legal because there is no way that they can take a "right" away from an American citizen. This landman stated that they do not have a value on what may or may not be below the surface, and therefore they cannot sell something that doesn't have a value nor can they take a "right" away from a person. Would anyone know how I can dispute this? My parents have asked my brother and I to help with the process of finding out.