This isn't part of the story but I thought I'd add it for fun because I was thinking about this a lot.
Harry's fatal faw is wraith: he is quick to anger and will rise if baited. This often presents itself in more than one book, it also shows in the form of jumping to conclusions based on bais (convinced that Malfoy was a Death Eater ((disregaurding the fact that he was)). Another opinion is that it is curiousity.
Ron's fatal flaw is envy: he if often jealous of Harry and his accomplishments in multiple books (the Triwizard Tournament and the Slug Club). This also might be attributed to inferiority complex and his fatal flaw could also be interpreted as that.
Hermione's fatal flaw is fear of failure: I thought about it and it seemed to me that one reason she reads so much is because she is afraid to not know and afraid that she won't succeed. Eg. When they got their O.W.L.s back, Hermione was so anxious about not being perfect and when she only got an E on one, she was exessivly distraught.
Bonus!
Arthur Weasley's fatal flaw is curiousity: he is curious about muggles to a fault and will take a risk to learn more about them. A famous case in myths is Pandora, she was told not to open something by the gods but it was too great a temptation.
Later edit: Also, also, actually, actually, I would like to point out that Pandora (as seen above) is NOT IN ANY WAY, SHAPE, OR FORM responsible for the whole box/pithos thing. The gods gave it to her for the explicit and inevitable concequence that she would open it. They tried to blame her for being curious. As the expression goes: curiosity killed the cat, but satisfaction brought it back. (please note that in this instance there was virtually no satisfaction to be had so the cat is probably still sickly and frail, maybe Frankenstein-esque, but I just like the expression and you beautiful beans should be curious or I'll steal your kidneys.)
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Big Three at Hogwarts
FantasyDoesn't follow the storyline, like, at all. Slight Trials of Apollo spoiler. Nico, Percy, and Thalia are sent to Hogwarts, they show up at Number 12 Grimmauld Place and meet part of the order. They head to Hogwarts with the very suspicious Golden...