@Arma_Artema
I mean it's been 145 years since Gensoukyou was sealed, pretty reasonable that not many people would know about the foundation of Gensoukyou after all that time. Especially since that information is kind of suppressed. Also it's mentioned that part of the village is made up of people who wander in and can't get out, and their descendants. Not like they would know what's up.
The important people know, like Akyuu and Reimu, but most people are kept in the dark. Probably, as mentioned in other manga, because if the villagers feel threatened they might rise up.
As for the Zashiki-Warashi, maybe Miyoi doesn't know that other Zashiki-Warashi are in the village.
Or maybe she thinks she'll be ostracized since she's been pretending to be human.
Or maybe her memory manipulating isn't typical of all Zashiki-Warashi and that makes it more difficult.