It’s got really really good jumpscares, and if that’s what you want this game is for you.
The problem is the game is a bit disjointed.
Basically the mc never says anything about how odd it is that his sister randomly looks like a zombie and screams at him.
At most, he asked “Why’s it so dark?” at one point in the game when someone turned out the lights. If you can question that, why can’t you question the jumpscare?
The first one made my heart skip a beat, it really was spooky. but it’s too often and as a result stopped being scary. At one point the jumpscares were so common they were expected, so when the end hit, I wasn’t that surprised with the jumpscare.
Personal theory is the sister fell down the stairs, or the side of the ledge near the stairs trying to scare her brother, hence the beginning of the game where she says “I was trying to scare you, I didn’t mean to fall.”
The reason the sis is never around or mentioned by the parents is because they know she’s dead in the box where you find a bear.
The reason mom is crying is because she’s still mourning the loss of her daughter. The father does send you away, saying the sis went to her room, not because she’s there, but because the family has given up on telling the mc she’s dead. So the dad, busy with work, just said “um… she went upstairs.” It’s to get you to go away. They’re probably both just waiting for you to process it.
At least, I think that’s the most sensible way to interpret things.