I have personally had a healthy chicken hang themselves on a kennel. twice now, it's horrifying. Make the slats too small for a head to go through, or use a solid side crate instead of the metal ones if possible. Fence fights are no "safer", I've experienced my share of those as well. I don't think there is ever a perfect answer.So i should let them sort it out right now while i can? I really love these chickens I rescued them together and I would really hate having to do anything bad to them.
I DO think letting them work it out is the fastest and simplest for everyone involved in this instance between already existing and healthy flock members.. It is what I would do, but you must decide what seems to make the most sense for your flock, yourself, and your long term goals.. with all the information you have available.
What gets set in place in the brooder gets overthrown often as the different birds hit different maturity points sooner or later.. the later developing ones naturally submit easier.. but eventually they all get equal hormone levels and gain their own confidence. So what's being described here does sound like part of the natural progression of things within a very dynamic pecking order, probably influenced by age and increasing daylight. It doesn't often come to this point in most small flocks, but it DOES happen. You haven't given enough time for one of them to back down just yet. It'll happen.
Scrapes, bumps, and bruises are inevitable when someone presents a challenge in this fashion.. I don't like it and I'm not condoning chicken fights at all, but we don't have to be scared when it happens.
I see you just posted a nice update, I hope they're through with it completely! No more angry birds, hug it out.