The Potter Twins and the Philosopher's Stone

A 'Harry Potter Siblings' Fanfiction. I was originally going to call this 'The Potter Children and the Philosopher's Stone' but two things stopped me: one, I already have a story called something very similar, and two, while there's three children, only two are involved in the first year's escapades because this is 'Harry has a twin sister' and 'Harry has a younger sister' put together! Yay.
Harry and Emma Potter are the Twins Who Lived, but they don't know it. And while their younger sister Rose claims to see their parents as ghostly figures sometimes, none of the three siblings know anything about what they are. When they find out, however, it doesn't take long for Harry and Emma to find themselves wondering whether staying at Privet Drive would have been better...