Complex sentence: Mummy and Raven are quite happy to live in a world without Christians, unlike the Splitters (George W. Bush among them) who strive to become as Christian as possible in order to ascend to Heaven during the Apocalypse.
Split into simpler sentences: Mummy and Raven are happy to live in a world without Christians, unlike Splitters. People who were left behind who strive to become as Christian as possible in order to ascend to Heaven during the Apocalypse.