Beardie seems to have broken leg? HELP!

My boyfriend just got two baby beardies about a week ago, and we listened to everything that our pet store told us about care and everything, we're feeding them regularly and they are eating and pooping and everything like normal.. However, at nighttime they seem to get more aggressive. He and I give them a lot of attention during the day, and they're both together when we do, and they've been together since they arrived at the pet store, but for some reason when we put them away for the last time at night and we settle into bed (they're in his bedroom), they will lay down for a little bit, and then one will get aggressive.. nipping at eachother (altho when we thought maybe it was because they were hungry, they wouldnt eat), and one will drive the other to the opposite side of the tank - its never the same one twice either.. Well, the other night they settled down and everything after a bit, and the next day we noticed that one of them isnt using their leg at all, and when it touches anything with it, it will flail it around as if it's in pain. When we watched them in the tank the other one kept going for that specific leg, to the point where we ended up separating the tank in two bc they were fighting so much.
I'm really worried that my baby is really hurt. Anybody know the reason they're nipping if it's not out of hunger? I'd heard only the grown ones are aggressive.. And what should I do about the leg? Should I bring it to the vet?

Hello and welcome to our group. Probably the leg was hurt by the other dragon. It isn't a good idea to have two housed in the same tank. Yes a vet vist might be in order. Please separate them before something worse happens.

They've already been split up, and we went and talked to the people at the pet store, and apparently were given bad advice by the guy who sold them to us... Thanks for your help