To the future, from the past

The marauders and lily travel forwards in time to harry Potters generation, to start their forth year.

What if?

What if Lily and James never died on Halloween? What if Harry's parents lived long enough to reach his second Birthday? What if Harry never lived at Number 4 Privet Drive with his Aunt, Uncle and Cousin? What if Sirius never went to Askaban for a crime he did not commit? What if Peter hadn't been made secret keepe...