all the problems between Jaye and Mc are his (and his wife's) responsibility, if there is a chance that Mc will let Jaye drown at sea it is his responsibility.
and I'm not talking about secret theories but directly recounted events
why don't Jaye and MC talk to each other for years leading, at least on Jaye's part, to an apparent hostility?
because Mc as a child decides not to accompany her to school any more and for this Jaye takes great offence.
but James and Sara know what happened and reassure MC that they'll work things out with Jaye, but they never do (Jaye only finds out through MC's mouth) and are content to watch as the two foster siblings grow more and more estranged from year to year, until the final breakup during the high school graduation party, and even after that they watch MC risk his life to travel the world and Jaye struggle in this failed relationship.
but then they have the courage to tell mc that they knew all about the feelings between the 2, but decided to remain neutral. the perfect parents.