Unique Abaddon Headcannons!
Abaddon wasn’t immediately detected by the father. Since the father is likely puritan, he may not have paid much attention to his kid or loved God more since priests aren’t meant to have distractions. We know that Abaddon gets attached to families easily, as seen in an Easter egg photo where he was with the previous family that lived in the hotel. I headcannon that he was there at least a year before he did something “unholy”, a minor mistake, that caused the execution. Upset, he pushed the dad off the cliff to survive.
I saw a fic where it wasn’t Abaddon that killed the father, but rather the boy. The boy realized that his father sealed him to the seamen and out of a fit of anger, betrayal, and sorrow, he charged at his father. The reason he hasn’t come out and revealed himself to the Freeling family or even tried to gain control is because he’s upset at what he’s done.
In the episode where Abaddon builds a nest and trashed the hotel because he looked in the mirror, he genuinely saw another version of himself. Either that or it’s based off the myth demons can’t see themselves due to not having a soul, but Abaddon has gained one!