Swollen joints can be caused by a number of things...accidents, inadequate nutrition, lack of vitamins, a slippery surface, bacteria, virus, infections.
You can use a homeopathic remedy called Thuja Occidentalis. That may help the swelling go down.
Is it's footpads swollen too? Is it acting...
Hmm, I think I see a barred rock (black and white striped). The speckled ones (I THINK) are speckled sussex. I'm not sure of that black and gold one or the all black ones.
I just read this thread:
https://www.backyardchickens.com/forum/viewtopic.php?id=3832
Now they are talking about adding babies to older ones, but there were a few ideas floating in here that sounded like it may also work for YOUR situation. Split the pen with chicken wire. The attacking...
Hmm. I would seperate the speckled ones then. If they're the culprits you may need to remove them so the rest are safe.
In my opinion the space doesn't look too crowded, so I'm not really sure what started it, but seperating them sounds like your only solution right now.
Also for the injured...