Justin Drew Bieber is the only child conceived by Jeremy Bieber and Patricia Lynn Mallette. They divorced after Justin's birth.
Jeremy (Justin's dad) has remarried and has two (2) children. The first child is named Jazmyn Kathleen Bieber, who was born on May 30, 2008. The second child's name is Jaxon Julian Bieber, who was born on November 20, 2009. They are his half-sister and half-brother.
He does not have a sister named Abbie. That is a rumor.