Jimmy Carter may be better remembered for his family, these days, than for his presidential record. And when Ronald Reagan's second son turned out to be a dancer, of all things, not long after Betty Ford's bout with alcoholism and drug addiction, while the world was learning about Jackie's unromantic life with Jack--well, the stage was set for an exhumation of presidential family embarrassments from George Washington's arm's-length relationship with his nagging mother onward. Unlike Barbara Kellerman's All the President's Kin (1981), Adler's gossip-fest has no sociological pretensions. It is also less seamy than other backstairs books that have gone the rounds. Not that anything good about presidential families comes to light here. Billy Carter is only the last in a line of troublesome brothers (Sam Houston Johnson was also a bigmouth, Abner McKinley had an unsavory rep). ""Many sisters of presidents. . .suffered from various degrees of neuroticism."" In-laws were a problem to the Kennedys and Grants. Even wives would seem, by this accounting, to be a dubious quantity. (Remember, before Jackie, Mary Todd Lincoln and Rachel Jackson.) ""Presidential sons have long felt the heat of public opprobrium."" Nor is the best of mothers sacrosanct: we even hear about elderly Ida Eisenhower's ""mental disorientation."" Drivel.