I like the idea of both Arthur and Faroe knowing that something is wrong about each other and that isn't their daughter/father. But, while its a tragedy for Arthur, its a horror movie for Faroe.
Think about it. While Arthur knows what happened and struggles with Faroe being grown up and not his little girl, Faroe knows nothing. To her, her father just returned from a 6 month "trip". He looks similar but he acts different. He grew his hair out and it grows at a unnaturally fast rate (headcannon). He's jumpy. He's constantly asking questions he should know the answer to. He writes with his left hand dispite being right-handed and his handwriting is different (Its easier for John to write than Arthur)(another headcanon). Hes secretive. He's ALWAYS wearing gloves. People call him the "Dead Man's Mouthpiece". He's always mumbling/talks to himself and she has no idea who John is (a name he says alot). His confidence and the way he moves through the world feels different. Hes disjointed and frantic at times. He sometimes starts talking about something (possibly a memory she doesn't remember or a fact he treats like second nature) but catches himself and stops from finishing the sentence. She swears he's always had yellow eyes but the memories feel fuzzy. Wrong.
Thats not even considering Parker and Eddie's deaths, Arthur's disappearance after said deaths, and in the short time he visited Daniel he talked about horrors, being followed, and trying to find a group of people (and Daniel also almost got killed).
Faroe's smart, she'll eventually put the pieces together. Maybe she might start diving into more supernatural mythologies to find a answer. I mean Astronomy has strong connections to different mythos. Perhaps she comes to the answer that Arthur is possessed by some spirit/entity (partially true) or that isn't him at all but a changeling/fey of some kind.
Imagine how horrifying that is. To have to act like a man who looks like your father but isn't your father is. To look into those yellow eyes that never seem to fully focus and convince yourself those are your fathers eyes. To find photos of your father from before the "trip" with your now dead uncle. Photos where your father had short hair, dark eyes, no gloves, and no scar across his neck.
