Sounds like it's time for chicken soup, chicken stew, chicken gumbo, chicken salad, chicken enchiladas, chicken sandwiches.....
In my opinion, if you don't want them to have access to your birds, you're going to have to stop free ranging. My guess would be that even if you adopt one of these feral roosters, if your chickens are free ranging, you will still have rooster fights because another one will come along wanting breeding rights to the hens and take on whatever breed of rooster you have as your flock master. It's only a guess, as I am not in your situation, but that's what roosters (well, males of any kind of animal, really) do. They take on other males to win the rights to the females.
Why not discard the Orphingtons in their entirety and adopt the local birds as your own? Keeping the Orphingtons at the expense of the locals is like a foreign power / alien invasion coming in and doing a little genocide because it is for some reason expedient. When you are displacing / removing those local birds you may be impacting neighbors used to those feral birds in a manner that is decidedly not neighborly. On the whole this process is playing out like what has been done so many times when we eradicate existing systems because they do not match our cookie cutter concept of how things should be.