Selena Gomez and mother Mandy Teefey attend the 2010 Hollywood Style Awards with The Palazzo Las Vegas, Klipsch, and FRS Healthy Energy at the Hammer Museum, Las Vegas, on December 12, 2010NEW YORK, N.Y. -- There’s a new reason to celebrate holiday season in Selena Gomez’s household — the star revealed her mom and stepfather are expecting a baby.On Friday, the star announced mom Mandy Teefey, 35, is pregnant.“Momma and Brian are finally letting me share the news,” she Tweeted. “My mommys carrying my baby brother or sister :).”Posting a photo of her mother, Mandy, and her stepfather, Brian Teefey, Selena Tweeted she was thrilled about the impending arrival. Click HERE to see the photo.“I’m the happiest girl in the world,” Selena wrote.And...