You can either use the original models of the bones or create copies of the bones. If you choose to use the original bones, be aware that the original animation will be overwritten, so you may wish to save this as a new scene. If you choose to make copies, you can copy just the bone models or the bone models and any children they may have (anatomical axes, locators etc). If you do not want to copy the children, check the "Don't copy children" box before hitting the "Duplicate" button. At this time, the still and mobile bone will be grouped together and you can move around in the scene.