Tell me what you think of my favorite combos!
[name_m]Joshua[/name_m] [name_m]Levi[/name_m] -
[name_m]Jason[/name_m] [name_m]Asher[/name_m] -
[name_m]Nathan[/name_m] [name_m]Joshua[/name_m] -
Also looking for suggestions! Boys names are so much harder than girls… [name_m]Favorite[/name_m] boys names: in my signature or https://nameberry.com/userlist/view/112039
[name_m]Nathan[/name_m] [name_m]Joshua[/name_m]. Would love to see [name_m]Levi[/name_m] [name_m]Joshua[/name_m].
[name_m]Joshua[/name_m] [name_m]Levi[/name_m] - classic, a boy with this name wouldn’t stick out name wise in just about any setting, will be as good today as it was and will be 8/10
[name_m]Jason[/name_m] [name_m]Asher[/name_m] - a bit more contemporary feeling, I like the flow 9/10
[name_m]Nathan[/name_m] [name_m]Joshua[/name_m] - doesn’t roll off the tongue as well as your other two choices 6/10
Other ideas inspired by yours:
[name_m]Asher[/name_m] [name_m]Nathaniel[/name_m]
[name_m]Tobias[/name_m] [name_m]Adrian[/name_m] (could be absolutely amazing with the right last name)
[name_m]Adrian[/name_m] [name_u]Bellamy[/name_u]
I agree boys are harder, happy hunting 
[name_m]Nathan[/name_m] [name_m]Joshua[/name_m] is my favorite, followed by [name_m]Joshua[/name_m] [name_m]Levi[/name_m]. [name_m]Jason[/name_m] [name_m]Asher[/name_m] is nice too, but doesn’t flow quite as well as the other 2, and [name_m]Jason[/name_m] feels a wee bit dated.
I second boyandgirl’s idea of [name_m]Levi[/name_m] [name_m]Joshua[/name_m]. I like [name_m]Joshua[/name_m] [name_m]Levi[/name_m] as much, but I prefer [name_m]Joshua[/name_m] in full to ‘[name_m]Josh[/name_m]’, so I like it better in the middle. 
[name_m]Asher[/name_m] [name_m]Nathaniel[/name_m] is also an excellent idea.