As Long As We're Together by Brianna Peppins

Paperback novel. A car accident takes their parents and leaves seven heartbroken kids on their own. Nova, 18, manages to convince the judge to give her temporary custody. If she can't keep her family running smoothly, they'll get to stay in their home. If not, they'll be placed into foster care. Nova will do whatever it takes to keep her family together, but Ariana refuses to take her advice.