With the frequent mentions of "Abraham" and "Jacob," I remembered the Biblical "Abraham, Isaac, and Jacob" - a phrase that shows up a lot in the Old Testament. The characters in the Miss Peregrine books are like those Biblical figures in that they're successive generations. The Biblical Abraham was the father of Isaac, and Isaac was the father of Jacob. This line of names is the same in the Miss Peregrine books, except for the middle one. In the books, Abraham was the father of Frank, who is the father of Jacob. Frank, unlike Abraham and Jacob, doesn't have peculiar powers, and he doesn't fit into that progression of Biblical names.
About three weeks after I first thought about those names, I happened to read something about how the Biblical Abraham and Jacob both had two names. Abraham was first named Abram, and Jacob is also called Israel. I don't think it's exactly the same situation for both figures (Abraham replaced Abram while Jacob and Israel are both used), but they do each have two names that they're known by, which got me thinking about duality. This brought me back to the Abraham and Jacob in the Miss Peregrine books. They too have a duality of sorts because they're part of the peculiar world and part of the normal world.
The cover of the book also has the signatures of the peculiar children (and a few other characters):
I noticed that Hugh's last name is Apiston:
It's an appropriate name because Hugh's peculiar power is the ability to control bees, and Apiston seems to come from apis, the Latin word for bee. It's still visible in the English word apiary.
