As you already have a large cage with a divider, one large UVB florescent tube fixture can be hung so it covers both sections of the cage...so all you really need is additional heat bulbs/fixtures.
It is possible for a male and female dragon to live together in the same cage and get along. But...the male will breed her every year and since he only has one female..he can easily over breed her. Bearded dragons are rather rough when it comes to mating, and when they bite the back of the neck of the female, they can tear the skin, causing injuries that will need to be treated to prevent infection.
The female then has the stress of producing eggs when means you have to ensure she gets plenty of food, extra calcium and vitamins, good basking time and exposure to UVB rays. She can't do this if she is being harassed by the male, chased around the cage etc. Producing eggs takes a toll on female's bodies..and laying multiple clutches in a season as bearded dragons do, often means little to no rest period between clutches...and a dragon can quickly lose calcium reserves due to the shelling process and suddenly suffer MBD, or other complications.
Even if the eggs are destroyed (frozen for 24 hours after being laid to 'kill' the embryo) then thrown out, there are many special things you need to do to ensure the health of your dragons. Having a proper egg laying bin for her to lay eggs in is necessary.. female dragons can retain eggs if they don't find a suitable nesting site...and 'holding in' their eggs gives a higher risk of egg binding...which can kill your dragon. Careful monitoring is needed on your part to notice if your dragon is having troubles passing eggs.
Other than breeding attempts bearded dragons don't always like to be with other bearded dragons. Even females housed together can suddenly turn on each other and you come home to find one of the dragons missing half their tail, toes, or even an entire limb.
Other than fighting and egg laying...other issues that can result from more than one dragon in each cage. Spread of disease/parasites. It is harder to monitor how often each dragon poops. If one develops internal parasites...both dragons have to be treated for it at the same time..which means taking two dragons to the vet, to be weighed so proper dosages of dewormer etc to be subscribed. Both dragons will have to be treated, and its harder to keep two dragons in the same cage from cross contaminating each other...if in separate cages, just have to make sure items used in one cage don't come in contact with items from the other cage...and only one dragon needs to be treated for internal parasites or most diseases. External parasites are likely to migrate into other cages anyway, if not caught fast enough..but better chance it not happening, if the dragons have no physical contact with each other.
Stress and dominance are other factors. Often when multiple dragons are housed together, one may dominate the other, taking the best basking sites, the bulk of the food, chase or otherwise harass its cage mate(s). With sub-adult dragons, this often results in one dragon growing faster than the other...and if not separated, the smaller dragon will eventually die..either from lack of food, parasite flare ups due to high levels of stressed or in extreme cases be eaten by the larger cage mate. Cocciadia, a common internal parasite in bearded dragons which is almost always present at some level in the gut of dragons will flare up to uncontrollable populations in a stressed dragon, especially prolonged periods of stress. Normally the dragon's natural gut flora keep cocciadia levels under control naturally so it is never a health risk for the dragon.
It may cost a few hundred dollars initially to have two separate cages...but treating a dragon for an injury or failure to thrive, egg binding etc. with a qualified vet can quickly cost more than the price of a second cage. All dragons should get at least an annual checkup and fecal done regardless, to ensure they are healthy and catch any problems early. An annual checkup with fecal per dragon may cost $40-$100 depending on the vet...but treating a sick dragon..can cost much more.
Oh and breeding bearded dragons and hatching their eggs...costs quite a bit. Bearded dragons are so prolific just doing it once for fun..isn't worth it. If you want to try breeding reptiles..buy a pair of crested or gargoyle geckos...or leopard geckos... these are easy to breed, don't take much room, and produce small clutches (2 eggs per clutch, multiple clutches per year...but not much more than 5-6 clutches, so 10-12 eggs per year).
A healthy single female bearded dragon in one season, can lay up to 25 eggs per clutch and as many as 6 clutches. Average...about 20 eggs per clutch and 3-4 clutches per year.
Baby bearded dragons eat ALOT of crickets... a single baby dragon for their first 2-3 months of age...(at which time they are old enough to be sold to new homes...) needs to be fed insects 3-4 times a day. Some can eat as many as 100 crickets of the appropriate size in a day spread over those 3-4 meals. Average is more like 50. Average clutch size..20 times average food eaten per day per baby, is 1000 crickets a day. Over a week, you are looking at 7000 crickets eaten by an average size clutch of bearded dragons...so breeding dragons is not something to be considered lightly. You can easily spend $45 or more per week just on crickets alone. To raise one clutch of babies till they are at minimum age and size to go to new homes can be $270 just for food alone. And I am being conservative on the cost. Just checking one big feeder insect company which includes shipping, it is $75 / 5000 crickets, so even assuming the clutch eats only 5000 instead of 7000 per week, thats $450 for feeding 20 baby dragons for 6 weeks.
Sorry for the long post, but just wanted to point out that it may seem easier and cheaper to house two dragons together...in the long run, it can end up costing much more.
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PHLdyPayne
