Okay, here’s my theory:
Devin and Liam are the same person. In the description of Liam, he grew up as an orphan. Who are Lost Boys? Boys who have been abandoned, they are lost. Devin grew up a lost boy but at some point, stopped being a Lost Boy and came back to fairytale land to become Liam, the Navy Captain.
I think this is a really good theory. And then Liam either fathers or adopts a young Killian and raises him, teaches him the sailing trade and then for some reason abandons Killian, though I’d wager not by choice.
I just hope that if this Liam guy does end up being Killian’s father, that the character’s name is actually William. Because only the first and last letters of those names are different. Though that would mean there’s no Eric, or Davy…but still, William and Killian just go so well together.
My headcanon still tells me that Killian is Eric and that Liam adopted Eric/Killian.