Bearded dragons are not social creatures. They need to have separate housing. The larger (older) dragon will eat your baby dragon given the chance. Both dragons will be much happier, healthier, and safer living separately. While it is great that you helped out the other dragon, keep in mind that each dragon should really live in a 40 breeder tank (minimum).
Here's a link to the care sheet from this forum. It is really helpful and full of lots of good information.
http://bearded-dragons.com/boards/index.php/topic,8.0.html