Awesome concept! I don't recommend using the term 'turncoats' though, collaborators on occupied territories usually use the term 'freedom fighters' and such since they wish to avoid feeling bad for the betrayal of their country and tend to think of their objective as fighting against their own government or the ideology thereof, rather than for the occupying nation. I recommend reading up on collaborators with axis powers during WW2 (especially armed movements) to get a clear picture of what I'm saying.
Use something like "Bretonian Free Corps" or "Bretonian Liberation Army" or something akin to that.
