Three musketeers + one

This book is based on a girl named Amanda, whose childhood is ruined when her father dies. She has two brothers: Cedric and Tony. She also has a twin brother Adam. Adam and Amanda are fifteen, Tony is 18, and Cedric is 21 making him the eldest. Out of four of them only two of them can drive and have job to support their sick mother who is admitted at a hospital. After their father died their mother is in a worse condition. Will they be able to pay her bills and buy her pills? Feed themselves?