A quick search through this forum will bring you a lot of answers, we've talked about this a lot, but I'll sum it up for you.
The only way to succesfully keep multiple beardies together is if they are all females. More than one male to a cage will result in fighting, injuries, and possibly death. Males an females together will result in breeding. Constant breeding at that, which can put enourmous stress on the female which can lead to so many things like she may stop eating, or she may get defensive and fight him off, injuring him. Also, since you're getting babies, they would breed long before she is ready, physically. Females should be about 1.5 years old before allowing them to become gravid. Also if you get them from the same breeder or pet store, you may end up with siblings and then you would be inbreeding them, which is REALLY bad. Even if you make sure to get all females, there is no guarantee they will get along, and you should be prepared to seperate them at any time.
Also, if I understand correctly, it sounds like you want to put the beardies in the same cage with the iguana? If that's the case it's a very bad idea. You shouldn't mix species. They need different husbandry conditions, and parasites that may be fine for one species may be hazardous to the other, and these are lizards which can be very territorial and agressive.
My honest opinion is that if you want the best, most stress-free environment for all your reptiles, give them each their own enclosure. Forcing them into the same space, whether with their own species or not, is stressful and unatural to them. It can potentially do a lot more harm than good.
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Amanda
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2.0 bearded dragons (Ocho / Domo-kun)

0.1 kingsnake (Rio)
1.0 ferret (Playstation)
1.0 cat (Wally)
0.1 dog (Tima)