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[Duke]

1. I believe that beardies will either get along or not. Age is no real indicator about their tolerance towards each other.
2. Depends on how many you have. Two or three should be fine all dropped into the tank. You still need to keep an eye on them to see who eats, and how much. If you can hand feed them then do it individually in their own tank. That's what I do.
3. A dog will most likely kill it on sight. Not sure about whether it scares the lizards. If they can run and hide then they might be fine, but if the dog starts scratching away trying to get to them, then you'll be introducing a massive amount of stress to the lizards. Then again it depends on te size of your dragons and dog. If it's a full grown adult, up against a chihuahua, then there might not be a problem.
4. Mine are still young, but I take them out of the tank once a day, just to give them a check over and see how they are going. If you want them as companions, then handle as much as possible (within reason - minimise stress...). Lack of contact will make them less tolerant to humans i.e. more flighty.
5. Depends if you want them to breed or not. Are you 100% sure you have a M/F pair? You may get complications in breeding periods and have to separate.