Abigail is lovely and unassuming. I like it a lot, but I can't say if its useable for you since I don't know said cousins and what their reactions would be.
However I do think of The Crucible, and the main character
Abigail Williams. But that's only probably because I'm studying it now, and they have been lots of famous Abigails so I wouldn't worry about that reference.
I really dislike the nn
Abby though, I don't know how inevitable that is.