Since some people seem to be under this assumption that Remilia/the SDM’s source of humans is from just snatching them from the human village…allow me to correct that by saying no. That can’t possibly be true, for two reasons. Both one that’s logically correct and one that’s canonically correct.
Logically, it makes no sense for that to be the case; if the mansion just snatched people from the village, Reimu would NOT stand for that, and nor would the villagers. Hell, the big reason why Flan is prohibited from going outside is that because when she DOES manage to get out, she sometimes attacks humans wantonly and destroys them so that not even a drop of blood is left. If her attacking people is such a big taboo, why would it be so alright for the mansion to just take humans from the village?
Secondly, I believe it’s been stated or at least implied in something ZUN had control over / input in, one of the mangas or in some sort of spinoff that either they’re supplied humans from the Outside World (by Yukari) or that they snatch up humans that wander in from the Outside World. I’m not sure which, but it’s one of the two.