That concept sounds really cool! Especially giving those with conflicting personality’s the ability to conflict in text (and progressively learn to get along should they so choose).
I actually was thinking of making my own CoG game with a similar mechanic so I feel especially strongly that it can and will work!
One thing I would be careful about is personality and lifestyle. Each new main character (spare the MC) can end up feeling just like the MC if a player is given the choice to dictate all of their moves. To curb this snag, I would suggest writing a base character idea for each additional main character (along with names and individual backstories) and keep with your unreliable narrator idea. Making any choices these characters get tailored to each main characters personality. For instance, say this person, let’s call him Ash, is gruff, icy, and reclusive. The reader is given the choice while in Ash’s POV to interact with their own MC and a few other main characters in the cast.
This choice might consist, at first, of what Ash was coming from doing—like gathering firewood, collecting water, finishing a short patrol, or waking from a nap. From there the choice moves to how they react to something the MC or another main character said. For Ash this would consist of pretending he didn’t hear it, snapping back, starting a fight, grunting their protest, or rolling their eyes. — all reactions that fit his personality while giving the reader the ability to morph their choices.
I might argue on behalf of giving the main customized MC, and only them, the choice to recollect with other main characters and let those interactions change the other main characters demeanor towards the main MC. (For the reason that it would feel less personal if you chose as another main character to forgive your customized MC quickly to avoid tension—tension which could serve as a good way to move the plot especially for a party of travelers forced to roam together, and work together, to gather needed aid in a raging war between their kingdoms.)
With that in mind, I think this is a great idea and that you should give it a go!