If you already know the middle name and have several first picked out, why don't you decide what his first name should be when you deliver him? I'm sure that can persuade you as well.
Josiah is fine, i have a nephew by that name
I like Josiah but since you already have a middle name see which one sounds better with his middle & last names
I have a middle name for him
Why not make one the first name and one the middle name?