I don't intend to come off at that way. One will be a respectful but practical individual, and the other will be more underhanded, and devious. Its not a matter of one being evil, or good. Its a matter of what they suggest. Light is Not Good, and Dark is not Evil essentially if you want tv tropes. Both combine together to form a being that essentially is the ultimate combat pragmatist but also is hard neutral in other words he doesn't care for morality. Victory is essential is his underline.
Again this is all just the initial idea we can change it as it comes along.
Makes a whole lot more sense now, the concept sounds fine to me. Most people who try to pull the yin-yang thing do go for good vs evil but the way you're putting it is a lot more acceptable so feel free to roll with it. Also, I don't know if it's your gig but if you want we have a discord where it's a lot easier to chat.