So if im understanding this right
Hakuma is the yuki onna (but clearly not a woman but his image pops up when they mention yuki onna sama), the fact no one else can see him but haru (the sacrifice) and her ghost cat seems rather telling.
I'm gonna throw a wild guess and say the noh masked creatures coming to kill haru are maybe the vengeful spirits of people previously sacrificed? Noh face of women, unnatural movements, long sharp nails.
And then the boys at the end presumably are the ones who know the truth about there being no shrine and likely no reason to kill seemingly the only "human" of the village. Perhaps they aren't snow people like it seems the rest of the village (barring haru) is.