Fan-magazine regulars and parents of hard-to-manage teenagers may be attracted to this tabloid-style look at the 29 Kennedy offspring. ""Not every Kennedy makes the headlines continually,"" says Bill Adler; ""There are even some. . . who have never been involved in bad press."" But Adler focuses on the headline-grabbers, which means that much of this is familiar. He tells of Joseph Kennedy's fortune and the family's penchant for sports; he wonders if Kennedys--in-laws and all--are male chauvinists. Then come individual chapters on Caroline, her assorted schools and current romance, and John, Jr., whose acting aspirations supposedly sent Jackie ""through the ceiling""; on Robert's stable oldest daughter Kathleen, and the notorious school and drug problems of his three oldest sons; and on Ted's son Edward, Jr., who lost his leg to cancer. The remaining cousins--some in school, some married, many with emotional problems--are wrapped up in one section. The Kennedys' ""triumphs and tragedies,"" gushes Adler, ""are our triumphs and tragedies."" Slick and glib and transient--but there's no gainsaying the built-in appeal.