Is possible that The Savior and The Destroyer is neither Sophie nor Josh, but the Swords. We know the incredible power this artifacts had, and have a mind of sorts (a good example is Clarent) and the fact that they (at least Clarent and Excalibur) can fuse together to be the Two that are One as Gilgamesh claimed it at the end of The Sorceress.
My theory is that that Sophie, Josh, Isis and Osiris will wield the swords in the final battle, the swords will fuse to become The One that is All and its sheer power will sink the city. A pair of these swords will become The Savior, while the other becomes The Destroyer. Sophie and Josh are the twins of the prophecy maybe because they are the only ones besides Isis and Osiris that can unleash the true potential of the Swords.