Complex sentence: After doing so, he began to develop his own beliefs, some of which were not supported by the established church--such beliefs being the existence of extraterrestrial life (aliens) and ghosts, souls either unable or unwilling to cross over.
Split into simpler sentences: After doing so, he began to develop his own beliefs, some of which that were not supported by the established church. Such beliefs being the existence of extraterrestrial life (aliens) and ghosts, souls either unable or unwilling to cross over.