Pedophiles gonna pedophile, you should be mad at your sister for acting like a retard. Don't throw that "SHE WAS 13" shit at me either, I remember being 13 and was capable of making rational decisions. Your parents and yourself also deserve sharp criticism for not realizing what was going on sooner. Hold you sister fucking accountable for shit before she grows into a defenseless gullible target of an adult.
Like Headliner said, nothing actually happened to your sister so chill the fuck out and stop trying to act like a badass on the internet.
When things go wrong, I sing along...it is the nature of the business...