Charlie Zerker is Josh Zerker's younger sister by 3 years. She had wanted to move out of her mum and dads house as soon as her close brother was kicked out of home 5 years ago. Neither of the siblings got on with their parents due to how strict they were and how their rules tore Josh and Charlie apart.
When Charlie finally turned 18 on December 1st, she was immediately trying to regain contact with her brother and trying to find a place for her to stay and it ends up they could be found in the same place. When she runs into Vik and Simon on a shopping trip, immediately she is welcomed to moving into the sidemen house.