Two different species of lizards, or even reptiles, should never be housed together. When there are two different species together you are risking serious injury and even death. Bearded dragons like to have their own space, and they don't like sharing with others, so they will start fights for territory and dominance. They both may have different age requirements, so that is another reason why you shouldn't house two different species together. There is also the risk of passing sickness and parasites (external and internal).