A SECRETIVE religious group that wields power in Washington, D.C. and other world capitals -- sounds like the basis for Dan Brown's next novel, but it's real. Jeff Sharlet, author of The Family: The Secret Fundamentalism at the Heart of American Power, has been following this group for years, even living at The Family's headquarters for a time. What he found is a group that justifies its pursuit of political power by claiming that it's for the kingdom of God.