PITTSBURGH — The story has more irony than a Greek tragedy. Three sisters from a devoutly Catholic family have seen their personal and political careers ruined by a scandal that began with, of all things, a letter to some nuns.Thursday's conviction of suspended Pennsylvania Supreme Court Justice Joan Orie Melvin along with her aide and sister, Janine Orie, on campaign corruption charges mean they might join a third sister — former state Sen. Jane Orie — in state prison. No sentencing date has been set.