Yan Tao isn't a bad concept, but I want him fleshed out a bit more. I feel like parts of his history, personality and traits are just webbing to put a few parts together you want in a character. I don't get a strong sense of identity from him, and I really do want one from each character. Also, 24 is still somewhat young for him to be a complete Airbending Master as well as have researched so many topics, especially spiritual knowledge. In this field, I would like you to tone back the Spiritualistic part, but you're free to highlight his academic talents. There are also Dai Li agents in this roleplay,specifically another PC, that aren't master-level, just close, but are still older with intense training. Mastering all thirty-six tiers is a sacred accomplishment, and I want to keep it such.
Jun is actually very similar to my Krane, albeit I see that you focus on his swordsmanship over bending. I can understand this, but what I dislike is the application of firebending onto metal. If lavabending, making molten rock, is a form of earthbending, it stands to reason that metalbending would unlock bending steel, including its heat. Bending itself is the manipulation of chi in unique ways that abide by a set of restrictions that are bending. I don't see firebending making a sword super-heated to the degree it could slice through more. Much like Krane using a sword-style, it uses the blade as an extension of the body and chi. Whether its firebending or airbending, it would result in the same effects. Now, there are ways I could imagine creating a similar effect, but I'm not allowing the direct superheating of metal. Aside from that, Jun is perfect. I read him and seen him as the older brother Krane could have had.
Sidenote: Change those damn unicorn Avatars.