I agree with @elanorelle completely! Anything goes in the second middle spot. I love [name_u]Declan[/name_u] and [name_f]Mila[/name_f], and both sound great with [name_u]Finn[/name_u].
Declan is a very handsome name.
Hades will not have a positive connotation for most people if they have an opinion.
I’m not well versed in mythology, and probably most people aren’t. So, from a layman’s perspective, the name is all negative to me. It has a cool sound, for sure, super edgy and interesting, but seems like a poor namesake. But again, that’s a layman’s perspective. If you know better and don’t care so much what the world at large might think, go for it. For what it’s worth, it would be a great name for a pet. A reptile or cat or pug or hamster Hades would be awesome in my book.
I was just watching a cartoon with my son and they were very clearly using Hades as a synonym for hell. I also have also heard the expression “hotter than Hades” used in the same way. For me, that association makes the name unusable, even though I understand that is not the original meaning.
I really like [name_m]Hadrien[/name_m], which has a similar sound. Or [name_u]Hayes[/name_u]. I like the idea of using another mythological name. [name_m]Jupiter[/name_m] is a guilty pleasure for me. And [name_m]Marcel[/name_m] (after [name_u]Mars[/name_u]) is high on my list. But I know there are some great Greek picks, too! Best of luck in choosing the name that’s right for you, I would love to hear what you decide on.