It really isn't a good idea to mix the fancy (Charlie) with the commons and comets. The fancy doesn't swim as well and will be out-competed for food. The
bio-load would also be a concern. If they have been in a pond, they could be anywhere from 3 inches to 12 inches (or more). If you had a tank that would be just for the two new ones, it might work, but I would be nervous about adding them to Charlie's tank. I don't think they would beat up on Charlie, but the shock to the tank could make him sick, as well as the food issue.