Saving Corey isn't implemented yet. Saving Khali results in an alternate ending, but was bugged and a variable was getting reset that shouldn't have. It might be fixed now or in the next update, but basically chose all the friendly Khali choices and then MC can go back and save her. And I'm honestly forgetting who Maya is at the moment, but I'm guessing it would also be an alternate ending.
This isn't directed at you specifically, but really just more a general commentary for everyone. There really aren't many branches to this game. All the actual branches just lead to an alternate early ending. The only two(four) real branches are if MC is resisting / agreeing with the killer, and if GG is resisting / agreeing with Jamal. This isn't an ORS, BaDIK, or most of the other top rated games, it has a pretty specific story the auther wants to tell, and there are only going to be slight variations in the scenes. Which is fine, I think a lot of the time developers end up with burnout because they're trying to BE those top rated game instead of sticking to their vision / ability.