From you current list I love [name_u]Florian[/name_u] and [name_m]Bastian[/name_m], and also quite like [name_m]Joseph[/name_m], [name_m]Caspian[/name_m], and [name_u]Camden[/name_u].
I don’t personally think [name_u]Emerson[/name_u]’s gender neutral usage is an issue worth giving it up if you both really like the name. I’m not a fan myself, but ultimately this is about what you and your partner like and can agree to.
With middles I have a few suggestions, largely linguistic variants of the family names you listed.
Some variations of [name_m]William[/name_m]:
[name_m]Wilhelm[/name_m]
[name_m]Wilkin[/name_m]
[name_m]Wilmot[/name_m]
[name_u]Liam[/name_u]
[name_m]Guillermo[/name_m]
[name_m]Guillem[/name_m]
[name_m]Gui[/name_m]
[name_m]Vilhelm[/name_m]
[name_m]Vilko[/name_m]
[name_m]Vilmos[/name_m]
[name_m]Ville[/name_m]
And so similar names like [name_m]Wilmer[/name_m], [name_m]Wilbur[/name_m], or a slight stretch with [name_u]Wilder[/name_u].
Some variations of [name_m]Joseph[/name_m]:
[name_m]Jose[/name_m]/José
[name_m]Joseba[/name_m]
[name_m]Josephus[/name_m]
[name_f]Joska[/name_f]
Joso
Guiseppe
Ioseph
Ioseb
[name_m]Yosef[/name_m]
[name_m]Youssef[/name_m]
Zef
And then similar sounding names like [name_m]Josias[/name_m]/Josiah/Josian, [name_m]Justus[/name_m], or [name_m]Jonas[/name_m].
And with [name_u]Douglas[/name_u], there really aren’t any language variants, BUT [name_u]Douglas[/name_u] originates from a place name- the name of a tributary of the river [name_m]Clyde[/name_m]. So [name_m]Clyde[/name_m], or even [name_u]River[/name_u], could be used to honor a [name_u]Douglas[/name_u] if you weren’t set on using the name itself.
Names that don’t share a meaning with [name_u]Douglas[/name_u], but resemble [name_u]Douglas[/name_u], include:
[name_m]Deangelo[/name_m]
[name_m]Deegan[/name_m]
[name_m]Digby[/name_m]
[name_m]Digory[/name_m]/Diggory
[name_m]Domingo[/name_m]
[name_m]Donaghue[/name_m]
[name_m]Dougherty[/name_m]
[name_m]Dugall[/name_m]
[name_m]Dwight[/name_m]
[name_m]Dalton[/name_m]
[name_u]Davis[/name_u]
[name_m]Dawson[/name_m]
[name_m]Dennis[/name_m]
[name_u]Dorian[/name_u]
[name_m]Duncan[/name_m]
[name_m]Dunston[/name_m]