There's a lot of ages to decide. Honestly, just guestimate based on how they look and their birth orders. Clara's kids ages end up a bit wonky, though. The older one should be 18-19, and the younger one should be 16-17. The problem is that the dialogue says Clara and Oscar moved away and cut ties "over 20 years ago", but both girls are MC's daughters, which would mean that the younger would have to be at least 20 years old. The math just doesn't quite work there.