[name_m]Humphrey[/name_m] “Humph” → [name_m]Humphrey[/name_m] is great - simultaneously “old man” (in a good way) and modern, it feels laidback but still substantial. In writing, “Humph” reminds me a lot of hump or harrumph, but I think spoken out loud it’s fine. I’ve also heard [name_m]Huck[/name_m] as a nickname for [name_m]Humphrey[/name_m] which I think is really cute.
[name_m]Barnaby[/name_m] / [name_m]Barnabas[/name_m] → both nice names! They’re not my personal style, but I think they work with your list.
[name_m]Lysander[/name_m] “Sandy” → [name_f]Love[/name_f] [name_m]Lysander[/name_m] and [name_m]Sandy[/name_m] is super sweet.
[name_m]Adrian[/name_m] “Ade” → I really like [name_m]Adrian[/name_m], though it’s definitely significantly more popular than the rest of your list (depending on where you live, I suppose). [name_f]Ade[/name_f] is intriguing, I’m not sure how I feel about it.
[name_m]Alistair[/name_m] “Sandy” → [name_m]Sandy[/name_m] doesn’t make as much sense as an [name_m]Alistair[/name_m] nickname to me. I assume it comes from [name_m]Alistair[/name_m] = [name_m]Alexander[/name_m], but it’s a bit of a stretch to me. I do really like [name_m]Alistair[/name_m] in full!
Of your other favorites, [name_m]Archibald[/name_m] “Archie” and [name_m]Vincent[/name_m] “Vinnie” are my favorites!
I think just about any combination of your names would make a good sibset. Lots of vintage names with cute nicknames. If I were to name three brothers right now, I’d say [name_m]Adrian[/name_m], [name_m]Vincent[/name_m], and [name_m]Humphrey[/name_m], or [name_m]Alistair[/name_m], [name_m]Humphrey[/name_m], and [name_m]Barnabas[/name_m]