Complex sentence: Marissa is moving in with the Cohens; actually the Gruesome Twosome-Caleb and Julie-are off to Europe, so Kirsten invited Marissa over.
Split into simpler sentences: Marissa is moving in with the Cohens. Actually the Gruesome Twosome, a.k.a. Caleb and Julie, are off to Europe, so Kirsten invited Marissa over.