Is 宵宮 considered 3 syllables or 4 syllables? I think everyone can agree that () has 4 mora. But one side says it has 4 syllables because there are 4 vowels. The other side says "Yoi" is similar to the in and thus only have 3 syllables. < Which side is right here?

[]{} takes four syllables.

I don’t know about the game(?) character, but as a normal word, it seems to be pronounced as {LHHH} according to NHK’s accent dictionary.

The same word is also read as {HLL}, and it can be written as in this case.

If it is a person’s last name, I would guess it is pronounced as {LHLL}.

The /oi/ sequence could sometimes sound like it constitutes one syllable (i.e. diphthong), as in {HLL}, but I think it is generally considered a combination of two syllables.