the ONLY time that two dragons should be in the same tank is for mating and you have to watch them to make sure they are ok. once the deed is done you remove the female.
this is the only time any two bearded dragons should ever under any circumstance be put into the same tank. dont care what any pet store tells you or any "reptile expert" says.
Germ has been doing this for years and knows his stuff, while i have only been a member here a short while i have learned from him and give him a great deal of respect, if he tells you somthing about bearded dragons its best to listen.