Though it is possible to house multiple species together, alot has to be taken into considering. Each animal's requirements for heat, food, hides, activity level, tolerance of other species in close proximity etc. All three of t hose lizards are diurnal, active during the day time, all need large enclosures with basking spots etc. Frilled dragons need alot more height than dragons, and get bigger than dragons. Uro's are about the same size as dragons (though the Egyptian uro is much larger) but required higher basking temps and are not all that great at climbing. This means having a low basking area for the uros close to 120F (can't remember their exact basking temp, but seem to recall it is around the 120F mark...or am I mixing uro's up with monitors?). As bearded dragon's don't mind a baskign temp around that range especially right after they wake up and eat, competition for basking space may occur. Though a higher basking spot may be used by the dragons instead, or be a place of contention between the frillies and dragons.
Besides competition for the best basking spots, uro's and bearded dragons have a very very similar diet, especialy when considering adult bearded dragons and any aged uro's. Uro's are vegetarians and eat the same greens as dragons. Thus, a food competition comes into play. Having multiple feeding bowls can help alleviate this but stress may still result in one or more animals of both species. Frillies, if I recall correctly, are complete insectivors (I could be wrong here, been awhile since I read up on frilly care requirements). Thus, the frillies will compete with the dragons for insects and given that frillies can be much larger than bearded dragons as adults (average bearded dragon is about 20" long. Average frilly 24" ) bearded dragons may be stressed and intimidated by teh larger frillies...especially if they flare up their frills.
Without going into possibilities of cross contamination of parasites and diseases, the three species you are thinking of putting together are probably not the best choices. Viviariums with multiple species are possible but care must be taking in choosing which species to put together. I can't think of any specices that would go with bearded dragons perfectly off hand. None reptile eating arboreal or desert dwelling snakes which don't get too big (3-4 feet) may live happily with a bearded dragon pair, but again, you will have to research these snakes, or other reptiles thoroughtly. Not just basic captive care requirements but their wild nature as well. How do they live and thrive in the wild? Secretive or highly aggressive species may not do well in an enclosed area with other species. Also, you have to ensure nothing can be eaten or will be eaten by other cage inhabitants.
Uro's and bearded dragons may be able to get along, if you make s ure th ere are sufficient basking/uvb bulbs to give all animals a wide choice (two basking spots near uvb lights per animal would be ideal). Visual obstructions to break direct line of sight between some basking spots will help 'isolate' them from eachother. Rocky outcrops, thick wooden branches, cork slabs etc, can be used to segregate the animals.
A pair of uros in with a pair of dragons would be plenty, no more than that. But I suggest making a separate enclosure for your uros, so they can be given their own home, if they or the dragons show signs of stress or combat. Don't put baby uro's in with teh dragons, as they will most likely become lunch. Full grown uros which are healthy and vet inspected for parasites etc, should be introduced, and monitored.
Though earlier I indicated it may not be a good ideal, I really wanted to point out all the possible problems and have you prepare for them first. I think uro's can be housed with bearded dragons but it is very hard to know for sure, as i have not done extensive research into uros. Having higher basking areas and feeding areas accessible easily by the dragons may help eliminate food competition and basking competition between the s pecies and individuals.
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PHLdyPayne