I just "finished" it.
I thought the story was a lot simpler than what I was expecting. I was hoping for an intense and difficult murder mystery and my character was a PI hired to find this out. Maybe some occult or horror sprinkled in. Well... that's what happens when you have completely unwarranted expectations.
Anyway, to answer your question:
I'm pretty sure there are twins. This is because one of them has a tattoo and the other doesn't. You can see this because I think on the 30th or so Hannah is wearing a blouse that shows her forearm and there's no tattoo. Also there's a bruise on one of those days which disappears the next day, indicating the switch happened. I believe at the end it's implied that Eve is in prison (or dead) and Hannah is now taking care of Sarah who is supposed to be Eve's thought-to-be-dead child (and is also you.). The wording "do you understand what your mother had to do now" wouldn't make sense otherwise.
There's also the question of how the hell could no one know there were two all this time but I think that can easily be chalked up to Eve talking nonsense. Not to mention the stuff about her parents and the cat and such have barely any bearing on this case, other than the fact that she probably murdered them too.
It's either that or Hannah / Eve deliberately made up that ridiculous story to cover up the murder and got away with it. I find that completely implausible given how there's no way the police would let her go after gathering plenty of circumstantial evidence to put her away. Though now that I think about it, between then and now is plenty of time for a jail sentence so maybe she's been released and found her daughter? Who even knows. I'm an Occam's Razor sort of guy though.
I think the nature of these kind of things is that at the end of the day you are only presented a certain amount of information after which everything else is speculation. In this case we literally only have 7 tapes worth of interviews to go by. Even then we don't have any facts, just a testimony of dubious nature. In the words of Sherlock Holmes,
'It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.'.
If this were reality, there are things we could do though to blow this open:
1. Do a bloody background check or two.
2. Confirm employment of both Hannah and Eve.
3. Interview the owners and patrons of the bars.
4. Read the police reports of this case.
5. Check out the house in question, especially the basement and the attic.
But since we can't... "it's just stories."
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As for the game itself. I thought it was interesting. Again, I was very intrigued by the way it was presented and was hoping for far more. Maybe some other people will see this and build upon it in the future. If there were more than just the interviews; being able to search through the databases for reports and stuff for example, then I think it would be brilliant. Maybe with a far more compelling case, but not completely fantastical. Grounded in reality but very difficult to piece together.
And let's be honest here. The twist of this story? It's not exactly original or unexpected is it? I think you'd have to be quite inexperienced in crime stories for this to be of any surprise.