Well, actually, some people still caponize roosters, so technically it could be done. It would definitely be a job for a veterinarian, probably wouldn't be cheap, and probably would be hard to find a vet willing to do it. Also, there may be a timing issue -- generally, it's my understanding with most animals that you really need to do this before they reach sexual maturity in order for it to stop problem behaviors. If it's done later, it cuts down on it somewhat but not entirely. I know that my second dog was neutered at 2 1/2 years for medical reasons, and he still did some behaviors typical of a male dog at times.
Your best bet would probably be to get a couple of nice pekin hens for the boys, and odds are they'll leave the chickens alone. If that doesn't work, you may have to separate them.