keeping multiple bearded dragons in one cage is a risk but its not all ways an imposible option. As we speak i have 2 bearded dragons(male and female) in a 55 gal breeder. there brother and sister and they have never been seperated in there lives(there 2 years old). i also have 4 bearded dragons(the male and 1 of the 3 females are siblings and all have never been apart in there lives, they are all just over 1.5 years old) in a 4'X2'X2' cage and they have no problems what so ever.
So pretty much if u want to put a pair together for then i sujest getting 2 females together because they will not breed(that could bring along many health problems which in most cases results in death) if u do want a male and female(If you are unexperienced with reptiles i would strongly sujest just keeping them in seperate cages) watch them very closley to see any dominance between them but u still will have to worry about dominance if u have 2 females together, just not as much.
i hope i could help you with these questions you have