Twin brother for Margo?

I am currently struggling to find the perfect name for this character of mine! It’s a collab w a friend who has named his twin sister [name_f]Margo[/name_f], and I absolutely require some link in sound or meaning or it will bother me for all of eternity. The other issue is, he and the rest of the royal family have white hair, and he has very bright blue eyes. I’m liking something aquatic as this is a shore-side kingdom and his twin’s name means pearl, but I’m open to anything that sounds right. Other meanings/themes I’m liking the idea of is something relative to gold or some other precious material. He’s the heir to the throne so he needs the perfect name, and I’m struggling to find a good match between classic/almost regal and befitting with spunky [name_f]Margo[/name_f]!

Edit: I had previously been thinking about the name Stellan for him if that helps with my taste at all, but I’ve fallen out of love with it for him. I’ve also liked the idea of Caspian, but my friend has a Caspian elsewhere and I have a Kasper in a third story, so it’s kind of a no-go.

Aurelius was my first thought! Shares the strong R sound with [name_f]Margo[/name_f], it means “golden” and I think it sounds regal! Some other ideas:

Edmund “rich protection”
[name_m]Edward[/name_m] “rich guard”
[name_m]Edwin[/name_m] “rich friend”
[name_m]Otto[/name_m] “wealth, fortune”
[name_m]Otmar[/name_m] “wealth, famous”
[name_m]Edgar[/name_m] “rich, spear”
[name_m]Arthur[/name_m] “bear, king”
[name_u]Basil[/name_u] “king”
[name_m]Kian[/name_m] “king, foundation, symbol of pride)
[name_m]Malik[/name_m] “king”
[name_m]Melchior[/name_m] “king, light”
[name_m]Regulus[/name_m] “king, little prince”
[name_u]Ryan[/name_u] “little king”
[name_u]Rory[/name_u] “red king”
[name_m]Aurelian[/name_m] “golden, gilded”
[name_m]Zlatan[/name_m] “gold”

Margo and [name_m]Kasper[/name_m] would be perfect together, sad you can’t use it!

How about:
[name_f]Margo[/name_f] + [name_u]Auburn[/name_u]
[name_f]Margo[/name_f] + [name_m]Judah[/name_m]
[name_f]Margo[/name_f] + [name_u]Jonah[/name_u]
[name_f]Margo[/name_f] + [name_u]Romy[/name_u]
[name_f]Margo[/name_f] + [name_m]Gordon[/name_m]
[name_f]Margo[/name_f] + [name_m]Goldwin[/name_m]

On the top of my head I can think of:
[name_u]Finn[/name_u] means white and fair
[name_m]Gavin[/name_m] means white hawk
Might sound too similar but how about [name_m]Marco[/name_m]? it derives from the roman god of mars and means warlike

wait…[name_f]Margo[/name_f] and [name_u]Marion[/name_u]!!! or [name_f]Margo[/name_f] and [name_u]August[/name_u].

Thought I would add some water themed ones as well
[name_u]Dylan[/name_u] meaning [name_m]Born[/name_m] from the [name_u]Ocean[/name_u] or [name_m]Son[/name_m] of the [name_u]Sea[/name_u]
[name_u]Morgan[/name_u] meaning [name_u]Sea[/name_u] Protector or [name_m]Captain[/name_m]
[name_f]Aquarius[/name_f] meaning Water Bearer
[name_u]Kai[/name_u] meaning ocean or shell
[name_m]Hector[/name_m] which is a dolphin
[name_u]Douglas[/name_u] meaning Dark Stream
[name_m]Earwyn[/name_m] meaning [name_u]Friend[/name_u] of the [name_u]Sea[/name_u]