Edit 1: It's like A Boy Named Sue or something.
Edit 2: Should I split this question into 2 posts so I can accept both answers? Huhuhu. I think I'll just accept 1 and bounty the other. It's a punishment for myself for not splitting up the post.
Apparently, the names of some of the characters in the anime/manga come from The Tale of the Bamboo Cutter where there's a male character there named 'Miyuki', namely Ōtomo no Miyuki (大納言大伴御行).
So we can see the kanji 御行 in both the Miyuki from Kaguya-sama and the Miyuki from The Tale of the Bamboo Cutter. Consistent, but...
...what's up with that? How can males be named Miyuki?
Actually, when I plug the kanji into nihongodera or google translate, what I get is, resp, Ōtomo onkō and Ō tomo on kō. There doesn't seem to be any 'miyuki' here. What's going on?