One thing I learned that usually works with cats that may apply in this case, is to feed them at the same time where they can't see each other. In the cats' case, they were fed on the opposite side of the door, so they could smell each other while they ate and then they associate the smell of the other cat with food. I don't know shit about chinchillas, but just brainstorming. Maybe put a towel over their cage bring em next to each other, and feed em?
The feeding component doesn't work the same with them as dogs or cats where you feed at a set time.
They eat hay which is kept available to them at all times, along with compressed pellets made from the same types of hay which help them grind their back molars.
I do give them hay and pellets and treats/chews at the same time, but they don't have mealtimes like a dog or cat might.
From what I can tell, this entire disagreement started when the white one injured his butt by dropping too hard into a bedding tray with wood chips.
Some of the chips got embedded in his skin like splinters and the pain of trying to dig them out and the constant chasing got the white one to the point where his fur was so thin I could see thru to his skin, which is very abnormal for chinchillas.
I had to take him into my own hands and work out his splinters with my fingers/nails, after which I kept him isolated the last few months to give him stress-free time away from the aggression so he could heal and rebuild his coat.
He's doing much better, but the first time I let him see his brothers there was a fight, and every time since when they even see each other thru the cage bars up close they will kack at eachother (shittalk) and try to bite.
They are like teenage boys at this point, I think I may have to just supervise their scuffling in open space outside of the cage and manage their aggression.
In the end I have two cages now, and I can just keep them apart if need be, but I really would prefer they live together.