I like [name]Gabriel[/name] best. It goes well with the others, it is a second 3 syllable name (which makes [name]Nathaniel[/name] seem less left out), and it starts with a different letter, so that each son will have his own first initial all to himself. Plus, [name]Gabriel[/name] is a beautiful name, and the nickname [name]Gabe[/name] is cute.