Pear bear! We love that book 
Anyway, fantastic list — these are the standouts for me:
[name_m]Lucian[/name_m]: [name_f]Lovely[/name_f], soft, unusual but widely familiar name (just like [name_m]Horatio[/name_m]). Several nice options for nicknames. Feels a tad “safer” than H but by no means bland!
[name_m]Ferdinand[/name_m]: I think this is really cool! The storybook connection is sweet, and it’s got a lot of weight and import to it which stands up well to H’s name. Ferdy is just adorable as a nn too!
[name_m]Benedict[/name_m]: Again, this has a very similar feel to your son’s name to me. Perhaps a tad on the religious side if you’re not (?) but such a strong, distinguished choice which is very underused.
[name_m]Severin[/name_m]: I love this name! It’s so spiky and funky and “don’t mess with me”.
[name_m]Corentin[/name_m]: Striking and once again very distinguished, but this one has a sweet, sensitive, romantic feel to it, as well as a storybook vibe (though I don’t know if there is a literary connection?) I love this one too.
[name_m]Marius[/name_m]: Gorgeous name! I love that they don’t shy away from “feminine” sounds in male names in continental Europe. I think this is a beautiful but also powerful choice that stands up well to big bro’s name.
[name_m]Peregrine[/name_m]: Another lovely storybook option with a really majestic, yet fun, feel to it. I love [name_m]Pip[/name_m] and [name_m]Pippin[/name_m] as nicknames for this — so bright and sweet!
I’m definitely drawn to longer names for you — H has a rather regal name to stand up to and I think his brother’s name would need some weight to it too.
My top 3 for you would be:
[name_m]Ferdinand[/name_m]
[name_m]Peregrine[/name_m]
[name_m]Corentin[/name_m]