I will absolutely guarantee you that if you have them housed together, this is absolutely 100% the reason that they aren't growing properly, as yes, they are stressing each other, constantly, every minute of every day. I know you aren't seeing it, no one ever does until they do become aggressive and hurt each other, which can happen on day number one, or at year number one, or year number 4 (if they both live that long). The fact that they haven't attacked each other yet means nothing, as actual aggression towards one another isn't the thing that typically kills one or both dragons when housed together.
I and many other experienced Dragon owners/breeders have seen this literally hundreds of times, and I myself alone have had this same conversation with people who have said exactly the same thing that you're saying right now, and after they separate the dragons to different tanks and move them to different rooms or at the very least stack them so they cannot see each other again, both dragons start to improve almost immediately.
Bearded Dragons in the wild are completely solitary lizards, they never, ever stay together, and you'll never see more than one at a time in the same exact place. The only time any dragons come together is when a male and a female come together to mate, and as soon as they are done doing that they separate. The female lays the eggs and leaves, and the babies hatch and separate. It's just how they live, and when we as pet owners force them to live together, not even in the vast Australian Desert but rather in a tiny little enclosed tank, we are putting them in a situation that is not only completely unnatural and uncomfortable to them, but that creates a constant, consistent stress on both or all of the dragons put together, and usually one is more stressed than the other. Either way, all dragons involved suffer greatly one way or another.
I've even see people who try to tell me that "my dragons love each other, they lay beside each other, lay on top of each other, lick each other, etc." and they have no idea that they are laying beside each other because one dragon is totally and completely dominating the other dragon. They silently compete for EVERYTHING, the best temperatures, the strongest UVB and UVA spots, the best insects, the best pieces of greens and veggies, the best spot to sleep, the best spot to climb and bask on, etc. Everything. And we can't see it, we don't live that way. But we need to try to understand this issue BEFORE it effects their physical health.
At a year old they've unfortunately both gone through 85% or more of their growth and development, but they still will continue to grow up until around 2 years old. And their bone density and muscle mass can always be improved, as can any neurological deficits that either of them have developed as a result of this constant stress and domination. I cannot tell you how many physically stunted Bearded Dragons we've seen on this forum, every day, every week, every month, hundreds and hundreds every year due to them being housed with another dragon and their well-meaning, well-intentioned owners being certain that this cohabitation is absolutely not the problem.
In this instance you have to ask yourself a few questions, if you truly care about your dragons as you say you do, which I'm very certain you do: Is it possible that keeping them together is the cause of their physical/health issues, since it completely and totally goes against the way they live in their natural, wild environment? Is it fair for me to force them to live together inside a little tank, when they don't ever live together in the vast, open, free Australian Desert? Is their UVB lighting adequate? Are their temperature zones within the proper ranges? Is their diet proper and adequate? Do I give them proper Calcium and Multivitamin supplementation? Are their lights on for a long enough photoperiod every single day? Am I using a solid substrate and not every using any harmful loose substrates? And if the answers to all of these questions about my husbandry are yes, and if I've made sure that the artificial environment that I've created for them is adequate and comfortable for them, then why at a year old are they both stunted in growth? Why are they having these issues when all of the external factors that can effect their growth and development are right in line with what they should be? And why are my 2 dragons having these issues, when other dragons kept in the same, well-controlled, well-maintained environments by themselves do not have these issues? What answer to their issues is left?
I'm not even going to ask you about your husbandry, or what
UVB light you have, how it is mounted, what your 3 temperature zones are, or what their diet/supplementation schedules are like, because I don't need to, as if they are housed together and are having growth and development issues as you've described, then I know what the problem is without question, and I know how to immediately fix the problem...you owe it to your dragons to at the very least set up a second tank with the same strong, adequate UVB lighting and the same correct temperature zones, keep them from being able to even see each other either by stacking their tanks or by putting one of them in an entirely separate room (this is the best option, as they can still smell and hear each other even if they can't see each other in the same room), and keeping them in their own, separate environments for at least a month, and seeing what happens. I would bet everything I own that they will greatly improve, almost immediately once separated and not feeling like they each have to constantly be competing for everything they need to live...