For 5 ask game: how about an au where zuko and aang are both the avatar
1- "how does that happen" well, Aang half died in the ice burg. The subsequent water and earth benders were noticably weaker than previous ones, though this helped the water bender hide from the fire nation, and led to the earth bender one being killed by them... Just as Ursa goes into labor for the first time. Unfortunately, Ozai wants to use his avatar son and is very disappointed when Zuko turns thirteen without a sign of airbending- the sages promised this boy was the avatar!
2- Zuko is invited to war meetings, but when he tries to speak he is silenced- when he is actually the avatar, master of elements, he will be allowed to advice, trusted, but not yet. He can sit in silence for only so long, and finally breaks to say they cannot sacrifice the children of the fire nation like that- and he is sent away to the sages, who suggest investigating the Air Temples and seeing if anything there sparks bending in him.
3- it does, the barest bit exploding when he gasped at the sight of the bodies, when he caught the glimpses of spirits in the corner of his eyes. Zuko can't stay here and orders the ship to take him to the southern water tribe instead, so he can unlock water bending. That doesn't work, (and the village says there's no water benders left) but it's marginally easier to practice fire and air bending outside of the graveyard the temple had become. He trains for years, knowing there is no point in returning home unless it's as the avatar.
4- and then one day, Katara wakes Aang up. Zuko gets close hoping the light are spirits that will help him learn water bending, and then we get to the first real problem of them both being the avatar: only one of them can be it at a time. So, when Aang starts bending, Zuko suddenly can't, unless he can overpower Aang and leave him unable to bend as well. (Which he only manages with the highest levels of anger) um, the avatar state is the opposite - if one of them goes into it, the other is dragged along.
5- Zuko is now chasing them because he wants an airbender and waterbender teacher, and also see if he can figure out from the spirits why his bending keeps vanishing. Iroh keeps asking him how he's going to actually convince them to teach him after he captures them, and Zuko says he'll just figure it out then. Katara thinks Aang is proof that awful firebending prince was only ever a mock Avatar and the bending vanishing is just a side effect of being in an ice burg for a century. Sokka thinks they're all crazy. And Aang actually figures out what's happening very early but no one believes it because "that's not how the avatar works" even though as 50% of the avatar, he should be considered an expert!
