When Jason says "My parents think they've lost the wrong kid", most think it means Jason thinks his rents think they rather loose Jason, but instead they lost Ali!
BUT,
I think his parents mean that they've lost the WRONG TWIN .
They might've lost Courtney instead of who everyone thinks they've lost... AKA Ali.
Meaning Ali is still alive and in hiding cos her parents want her to be safe after what happened to their other kid.