You probably want to get a beta; your tenses don't always match and you use the wrong words in a few places ("AN" instead of "AND"). Also your conversation between Dumbledore and Petunia was stilted. Perhaps try reading it out loud to yourself to see how it flows.
But it's an interesting story.
(My guess - Romana is Lily's grandmother, but Petunia was adopted or a half sister).
Thanks for writing this.
Tom A.