Im horrible with names so this is a bit confusing. So when they were in the wreck, his body was paralized/dying and couldnt move, but he would live he just had to regnenerate, but instead of waiting he "had" to switch bodies with his son whos body wasnt as damaged so that he could save Mc because I guess if MC is not aware of his imortality then his body wont regenerate. And in switching bodies with his son, he died because the son didnt have regeneration abilities. If this is correct then their regenerating abilites comes from something in there brain/consciences.