To be a member of a tribe you have to be registered with that tribe. Many, like the Cherokee, have pretty much closed their roles to new enrolees. Anyone can live on a 'reservation' however. Native Americans do not own outright all the land included in their 'reservations' land. The tribe may own tracts of it that are exclusively for NAs but most ownership of land rights still beling to the state, federal, or nearest city govt or private. In other words even non-NAs can buy and sell property in lands designated as 'reservation' land unless the tribe specifically holds title to it. Pretty much all of Oklahoma is a reservation for one tribe or another. They have no control over land rights unless theyve paid money for it and hold a federally legal title to it.