They are two years apart, both underage. Then when he turned 18, suddenly that makes it different? She had been living with them for an extended period of time and having consensual sex while both were minors. When she became pregnant, the family didn’t want her to keep the pregnancy, where the options were to either get an abortion (valid, especially for 16-18 Y/Os still wholly dependent on the parents financially and for shelter) or her going back to her family’s Idaho house and having the baby. She chose the former. That’s not kidnapping, that’s a choice.