Wilson Phillips, the fresh-faced celebrity offspring who produced one of the most successful debut record albums in history, have apparently splintered into solo careers.Although the trio’s SBK Records label won’t rule out future projects, there are no plans for recording beyond a proposed Christmas music collection. All three members of Wilson Phillips are signed as solo artists to EMI Music, the parent corporation of SBK Records. The self-titled Wilson Phillips debut album sold more than 6 million copies in the U.S. and produced three No. 1 singles: “Hold On,”"Release Me” and “You’re in Love,” along with the No. 4 hit “Impulsive” and a No. 12, “The Dream Is Still Alive.” Nominated for four 1990 Grammy Awards, including album of the year, the group was known for its lush harmonies, squeaky clean pop songs and videogenic appeal. But its sophomore effort, “Shadows and Light,” released last year, was not as successful. Between albums, Wilson Phillips had changed managers and aimed for a more sophisticated image, a move many industry second-guessers felt clashed with the group’s established appeal among young female teenagers. The first two singles from “Shadows and Light,”"Give it Up” and “You Won’t See Me Cry,” barely nudged into the Top 40 and any chance to build momentum was killed when the group’s proposed summer tour was deep-sixed. Despite selling over a million units, the huge marketing costs left “Shadows and Light” on the list of last year’s biggest disappointments. Sources say Chynna Phillips, daughter of actress Michelle Phillips and songwriter John Phillips, is now exploring a film career, while Carnie and Wendy Wilson began work last week on their first recorded collaboration with father Brian Wilson, the Beach Boys songwriter who is recording his next solo album. Carnie and Wendy Wilson had explored their sometimes-troubled relationship with their father on “Flesh and Blood,” a song from the second album. Charles Koppelman, chairman of the EMI Records Group North America, said yesterday the state of Wilson Phillips “depends on how you look at it. If I were a betting man, I believe they will be recording together again at some future point.” However, Koppelman acknowledged that the three are now working on solo projects. He did hold out hope that the triowould reunite for a Christmas album that would, if it happens, be recorded this summer.