I agree on the spelling and formatting issue. Also, I don't like your Sirius, Remus and Snape and fear the role they are going to play.
I don't agree on the prologue issue. It's perfectly possible to start a story like this.
But you'll have to come with a very good explanation for Jack being/seeming to be Harry. Halloween is quite old, ergo Jack is quite old (hmm, except perhaps if you played the games it seems if I read it right on Wikipedia, but whatever). And what with Sally, is she for some reason Luna then? Otherwise it is quite original and if you think about it, not that far-fetched. But only when Harry is the adopted son of Jack and Sally when Jack came by the house of the Potters on Halloween when they died and took Harry away, which explains the "we found him" too.