second book of Harry Potter fanfic

Orphan Twins. One Sister lives in peace. The other is trained for war. Magic has been missing for centuries, but a prophecy foretells of its return. Livia and Vera hold the key to its unlocking but neither know the other exists, until a golden mirror appears in their dreams. The reflection reveals a startling truth, and the sisters begin to question everything they've been told. Vera, a feared assassin, is tasked with hunting her twin down. And Livia must find a way to stop her before two kingdoms are destroyed. Blood will war against blood. And a choice must be made.

Harry has a younger twin sister, and this is their life.

When a down-to-earth Paris baker and a soon to be princess discover they look like twins,they hatch a Christmastime plan to trade places

Francis and Arthur adopt twins! But one of them just doesn't feel right to Arthur. Francis won't believe him and it's tearing them apart. But maybe Arthur's history with mythical studies will help them through it.