

That’s an old source that misses one crucial detail. One twin is going to be the incarnation of Raava and the other Vaatu. So… more like avatar and anti-avatar.
Personally I would have given the anti-avatar different powers from the avatar if I was in charge of the show, just so it doesn’t feel like a “face yourself” level of Super Smash Bros.
Tom Nook be making those deals you can’t refuse.