I love Elijah for a boy :) I'm not too fond of your others, but Elias isn't THAT bad. Eli is a super cute nick name for either, though!
Middles for Elijah:
Elijah Thomas
Elijah Oliver
Elijah James
Elijah Alexander
As far as the girl's name's go, I like them all, but Natalie is my favorite. It's so timeless and feminine, I just love it! Lucy Helen is also cute, but Helen isn't really my style. But Lucy is adorable, no doubt.
Middles for Natalie and Lucy:
Natalie Lynn
Natalie Claire- LOVE IT!
Natalie Kate
Natalie Olivia
Natalie Grace
Lucy Lee
Lucy Elizabeth
Lucy Paige
I'm just going to throw out some other names I think you may also like-
boys:
Baylor, Jackson, Preston, Oliver, Thomas.
girls:
Audrey, Ainsley, Amelia, Presley.
I hope I was able to help! Good luck! :)