Firstly, apart from the jump scares, the sound design is where your game really shines. the music and the ambient noises were very well placed and have the most potential to carry over into future projects. Good job!
I do think the jump scares took away from the game rather than added to it. The house level had the most Silent Hill-like atmosphere, and the door jump-scare was actually quite good. The third Chapter seemed out of place and lacking context- it was also kind of confusing to navigate.
I think the idea of interconnected stories is a good one, but you need to flesh it out more. Firstly, you have to decide what your game is about. What was this game about? The one common theme I could find was that the characters' realities in their minds do not match the reality of the world they inhabit. Once you have that core concept, you need to really dig into what is scary about that. The thing about horror games is that they are narrative games- you're telling a story that the player is unfolding as they engage with the game.
For an interconnected story, there would need to be not only a common theme, but an adjoining narrative. If it all takes place in the same world, that's cool, but then they could be separate games. For example: what if the child from Chapter 1 is the son of the couple in Chapter 2? How could the narrative and gameplay change to reflect this?
There's also the issue of the mental health aspects in the game, and how mental health can easily be stigmatized in media. I think you'll find more concepts to play with if you focus on the theme you've started of "what is reality, and is what I think to be true actually true?". That's a very interesting concept, and what I liked most about your game besides the sound design. And it's a theme that can easily be about mental health, or it can be about alternate realities, hauntings, possessions, etc.
Sorry I've written like 89 paragraphs or whatever lol. You'll continue to improve for as long as you keep at it, and you have some solid skills to build on. Good luck!