Having dealt with teenage relationships, I can totally see it. Korra is a bull in a china shop. Mako doesn't want to offend either of them, he feels for both of them, and is a ****ing idiot. Asami was hurt (emotionally), but the two of them worked it out (especially, IIRC, after season 2 or 3, where they were pen pals while Korra was recuperating).
And, right now, nothing is more natural than the relationship between Tenzin and his siblings.