Difference in size - together?
NEVER EVER let dragons with a big size difference be together! Never! With babies the difference shall never be more than ½ inch or so, with adults never more than 2 inches. It is the size of the body that is important. If one of the dragons has a shorter tail it isn't that important. If the size difference is big, the bigger one can kill the smaller one. Too many times I have read about these unnecessary "accidents" (I don't call it an accident - since the owner SHOULD have known better…). Bearded dragons hunt their food and attacks everything that can be considered food or rivals. Or - they fight because one of them is big and dominant. That's just the way it is. Even if the bigger dragon doesn't kill (and eat) the smaller one it can hurt it badly.
Never take a chance
Never take a chance on this - even if it seems to work in the beginning. Don't even bring them out to take a cute photo. An accident can happen in a split second and then it will be too late. If you have dragons in different sizes - you MUST keep them in different cages until they are the same size. When I see different sized dragons together I always tell the owner what could happen. Too often I get the answer "Oh no, my dragons loves each other, the bigger one is so nice to the smaller"… They don't believe me. Then (not too seldom) I get an email from a desperate owner that ask me what to do since the big one has hurt the small one - badly. I have seen several pictures of hurt dragons - and it is NOT a pretty sight.
One beardie ate another
At a forum online I read a message from an owner that couldn't find his small dragon. The little dragon was around 5-6 inches and was kept with a bigger dragon around 9-10 inches. The owner joked about it and asked if the big one could have eaten the little one. Unfortunately it turned out to be the case - and it wasn't that funny anymore… Another problem was that the bigger one nearly died from this - his pray was far too large. So - please, please - think about this BEFORE anything happens!
If an accident happens
If an accident happens - take the hurt dragon to the vet - A.S.A.P. Do NOT waste precious time to ask at forums what to do. Don't wait to see "what will happen". You made a mistake and now you have to help your dragon. Call a vet and get there as soon as you can. Maybe it isn't too late to help your dragon. If the dragon is badly hurt it might have to be put to sleep to stop the suffering. A vet can help you with that if he or she can't cure your dragon.
I know, I know… I keep nagging about this - but I really want the best for your dragons - and for you. You will never forgive yourself if anything happens just because YOU were ignorant and didn't listen to good advice… I know… because I have a very tragic memory of a story like this. Please read more at "In memory of Hexxen" - and learn from MY mistake!