I watched the stream live and immediately after temporarily took the game down to rewrite large portions of the story. If the other comments are not as harsh on the story, it's entirely thanks to your stream feedback. (Obviously I am not asking you to try the updated versions or even look at this game ever again.) I'd never heard of "beyond 2 souls" before your comment, so I had thought "ghost resents someone for wasting their life because it could have been their life instead" sounded like a cute story idea, but seeing as how it's a cliche that's been done before, I'll go figure something else to do. I previously joked to you elsewhere that the dad was the self-insert character in response to the stream comment that the girl came off as a self-insert, but the twins are not based on my own kids, so I'm perfectly fine trashing them and figuring out a different story entirely.
I think "ghost regretting *something*" is a very common trope for a ghost story and also a reason for the ghost for not moving on to the afterlife, at least in common folklore. I even recall one such story from my childhood - it was about a kid who fell down the elevator shaft in an abandoned building, so now he haunted the building scaring off other kids (us) so that we don't fall.
I'm also a bit of a junkie for "ghost investigations" slop on youtube, so... yeah.
I'm not sure if there are many games exploring the whole theme of ghosts being attached to the world, but I can name at least 2. One is "Beyond: 2 Souls" (used to be a playstation exclusive, dunno about now. It's one of those "movie games" so you won't miss much if you watch it on youtube), the other is "Murdered: Soul Suspect" where you basically play as a ghost detective. I definitely think this idea can be explored, but the "it's actually a ghost who regrets something" is not a very good twist imo. Or maybe you were too much in a hurry to set it up & reveal? I dunno. I might have worked if the player was left doubting the nature of the kid for a bit longer. Like - let's say the girl and the kid had a spat, so the girl went "I'm gonna unimagine you" and the kid actually disappeared/flickered for a moment? Could also work for building their relationship. The reveal felt a bit too straightforward.
I also feel like you have potential for multiple storylines in your current game, and that could serve as a backup for annoying picky bastards like me. For instance - you could expand a bit on dad and why he's alone, why he cares about the girl. Maybe get a bit into some old relationship drama? Maybe he feels guilt? Maybe he's not just having a 1000 yard stare from working soul sucking dead end job, but trying to catch a glimpse of the ghost who he knows is there right next to his daughter? There's also a good opportunity to pivot into the scifi storyline that you kinda started setting up in the basement. Was dad involved or was he an involuntary subject? And what was happening in the basement? If the notes were a bit more coherent and expanded more on the universe/"something bigger" - that would've been really cool. "Oh, you're not interested in dead kid story? Here's the evil science plot story to have you hooked". Something like that.
Bear in mind I'm not a writer and I'm ESL, so take all that I said with a grain of salt. Just thinking out loud for what could have been.
Also I still stand by the "bladerunner 2" ending comment, though not everyone finds such endings enjoyable. But I do love a good subversion. But it also has to be set up correctly.
In any case - I'll definitely check the game out some time later again, I'm curious about your progress.
And thank god it was a joke, I actually felt bad for a second lol