Dursleys

We all know that when He-Who-Must-Not-Be-Names attacked Godric hollow Lilly and James died while harry lived and was sent to the Dursleys, but what if Harry's parents lived? What if Harry had a twin who was mistaken for the Boy-Who-Lived and they sent to him to the Dursleys so they could focus on his brother, what if the Dursleys liked magic? And what if dudley could do magic? And lastly what if the potters thought they could get harry back when he turned 11? But what if he doesn't want to go back?