How much do we know about the Romanian clan?

I've searched through Breaking Dawn and all I can find about them is that there's two of them: Stefan and Vladimir and that their empire was overthrown দ্বারা the Volturi 1500 years ago.

So we know that they tried to overthrow the Volturi, but do we know when and how it went down? Does anyone know their lineage, where they live, their story, etc?