I'm so sorry that i have not buy the game,in fact i "play" the game through the game videos. I'm very interested in the game plot, however,it doesn't support Chinese,so I can only know the story through the videos With subtitles.
My Immature speculation is that:The guests are insect.
First,the protagonist once said:" The land has grown soggy too.All the large species of animals have died out.all that is left are the numerous species of insects. ' and one of the diary's pages said" They are real. But not as they appear. You see them like that because you're in a state of somndence' and in fact in the late game the protagonist will say some words like: they are live、i should think of them as something else(Sorry I didn't remember the complete sentence),and guests come form the forest.So,Is there anything live in the forest except the protagonist and insects?
And,if you think about it carefully,you will find that the guests' some habits are as good as insects.For example,when you turn on the bulb,the guests will find you,and when you hide,although you're more than half exposed,they sometimes still cannot find you.The big eye on the wall prefer to appear in the bright room. They can go through the locked door and wall,up and down the stairs without ladder.
The insects are Phototaxis,it will be attracted by light,so it will be attracted by the bulb,the candle on your hand,when you hide,the candle don't give off light.This is why how guests search for you just like taking a chance.the insects are small so they can get in by every opening.they can crawling along the wall,floor,furniture,anything adjacent to them.Some of them can fly through the window,the little ♥♥♥♥♥......don't forget that the house is very very old.Maybe this is why the plot always mentions that restore the house,mend every gap.
When you are walking in the forest,you will not find any insects.But do you notice the woods in the distance as background?If you watch them carefully,you will find eyes:a large number of eyes on the trees.What are they represents?
I have some more evidence.The protagonist once said some words to the effect that little lives have been here.Somethings slap the window(the insects will do that). The shadow of insects will flash through the home page of this game website,and tow of the Wallpapers in the website appear the insects,the Wallpaper 1:seven insects surround the most big eye's pupil,the Wallpaper 3:some insects appear in the cloud,and there are some eyeballs in the cloud too.But the insects have never been appeared in the game.
My English is not good,so there will be many grammar mistakes and other bad things.All of this is my personal opinion,it may be wrong,and i am not sure that no one think the same before.Thanks for your read.