Josh almost turned bad in the Magician, and he's likely to turn bad anyways.
The prophecy went like "One to save the Earth, and one to destroy it"
So far, Sophie doesn't look like she's influenced under Dee and the Dark Elders.
And remember, Athena isn't going to be the Enchantress. She's an Elder of War and Wisdom in Greek Mythology, and certainly not a Humani.
Awakened/Immortal humani have done it so far (Flamel, Dee, Perenelle, etc.) and probably will for the rest of the series.