I love Luke Nathaniel! It sounds so handsome. Luke Thomas is a great combo too.
Luke Giovanni is great. Does it matter to you that he will have the same first initial as his brother Levi?
I also like:
David Giovanni or David Samuel
Adam Giovanni or Adam Samuel
Mark Giovanni or Mark Samuel
No, it doesn't bother me that we will have two L initials in the house. :) Still working on hubby to go with Giovanni for the middle name spot, nit sure why he doesn't want to. Andrew, is nice, but we have a close family relative with that name...