Complex sentence: Residence in Adelphi is open only to members of the Adelphi Organization, "which continues to teach the tenets of Lemurian Philosophy and the eventual occurrence of cataclysmic earth changes, though they removed specific dates from the current 2000 edition of" The Ultimate Frontier.
Split into simpler sentences: Residence in Adelphi is open only to members of the Adelphi Organization, which continues to teach the tenets of Lemurian Philosophy and the eventual occurrence of cataclysmic earth changes. In 2000, the Adelphi Organization removed specific dates from the current edition of The Ultimate Frontier.