Females can get along with each other when housed together but there is no guarantee they will always get along. Two 8" babies will be ok in a 20 gal tank for a few months but not for much longer. A 35 gal long ( err, roughly 3'long by 17"
will be better for two 8" babies till both are about 14". A 4'x2 tank is too small for two adult dragons regardless if they get along or not. That size tank is the minimum for a single adult dragon. To add another dragon, you will need to add another foot (at least) to either the width or length of the cage (ie 5'x2' or 4'x3').
When dragons are introduced, it should be done on 'neutral' ground to see how they initially react to each other. Any signs of aggression will require immediate separation. Arm waving, head bobbing, gaping and mock lunges are alright but direct attacking or biting, definitely means separation. Having two dragons in the same tank can cause many not so obvious signs indicating the dragons are not getting along. Competition for good basking sites, food, etc can result in one dragon failing to grow as well as the other. If either dragon fails to grow as fast as the other, should be separated. If one dragon always hides, doesn't bask very much, doesn't eat as often etc, should be separated.
I also recommend that both dragons be tested for parasites before introducing them into the same cage. This ensures both are completely healthy and parasite free. When dragons are housed together, what one has/catches or develops, will infect the other in very short time. So if one has parasites, the other will get parasites. Thus when housed together, both will have to be treated for the same ailment, be it parasites or some other contagious disease.
In my opinion, multiple dragons should be housed in as large a cage as possible, beyond the minimum recommended size. The more room both have, the better. This way they can keep their distance from each other when they wish to. Thus, cages with more than one dragon should have multiple basking sites, hides, feed dishes (placed a good distance from each other), etc.
Also, very young dragons are not as easily sexed as older dragons. Many breeders indicate their young (6"-10"
babies are a certain sex but I don't feel this is 100% accurate. We all make mistakes and bearded dragons are not that easily sexed when under a foot in length and about 6 months old or older. Thus your pair of females may turn out to be two males or a male and female. If this turns out to be the case, even if they are getting along and in a sufficiently big cage, you will have to separate them. Males once they hit puberty (around 6-8 months of age) will fight. Fighting males can seriously injure each other and if left together, this can result in one or both dying from wounds or at best, loss of tails and toes, sometimes even limbs. A male and female pair will often result in the male trying to mate with the female, sometimes inflicting wounds upon her in his efforts and risking getting her pregnant. A female under 12 months being pregnant can cause many health problems, including higher chance of egg binding, stunted growth and MBD.
Though having dragons together in the same cage does increase social interactions between them, the risks involved, to me, isn't worth it. Dragons living together do show more of the arm waving and head bobbing than those living in separate cages, but with the risk of one or the other not eating properly, spreading of diseases, tail/toe nips, fighting, early pregnancies, etc. doesn't seem worth it.
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PHLdyPayne