A month or so ago we were offered two bearded dragons, complete with vivariums. Their current owner had little time to care for them properly and although we have little spare room in our house, we agreed. They were being kept together inside one vivarium, separated by a mesh wall. This was because not both vivariums had suitable heating and lighting.
Apart from having little room to roam around, both are male beardies and were constantly displaying dominance and stressing each other out. Like most lizards, bearded dragons are solitary creatures and only approach others during breeding.