Here are some posts with hunches regarding F's family that I found. These are sorted in the order they were posted, of course.
F having siblings:
The Wayhaven Chronicles: Book One (Discussion) FAQ Located on Post 2 - #4688 by Mewsly
F being a middle-child:
The Wayhaven Chronicles: Book One (Discussion) FAQ Located on Post 2 - #4700 by rose-court
and
F’s family not being particularly… ‘friendly’ towards humans:
The Wayhaven Chronicles: Book One (Discussion) FAQ Located on Post 2 - #4706 by Mewsly
Alternatively, F’s family being super-cool and laid back:
The Wayhaven Chronicles: Book One (Discussion) FAQ Located on Post 2 - #4707 by anon90085413
This is not a hunch, but Sera confirming that F’s family have absolutely no clue as to where they might be or how they simply vanished:
The Wayhaven Chronicles: Book One (Discussion) FAQ Located on Post 2 - #4884 by Mewsly
and
The Wayhaven Chronicles: Book One (Discussion) FAQ Located on Post 2 - #4891 by Seraphinite
F’s family probably assuming that they’re dead:
The Wayhaven Chronicles: Book One (Discussion) FAQ Located on Post 2 - #4894 by Hannah_Minger
God, I hope I did it right. I’m sorry if I missed any significant posts but I tried to keep them limited to the criteria you suggested and did not include posts that were made obviously in jest. Not sure how I feel about having to read through all that angst-content in the previous thread through, phew.