HI IM SORRY FOR THE LATE RESPONSE!! I don't usually check up on Itch.Io due to it being my christmas break, but I'll try to respond to all of your questions.
1.) I've been procrastinating on fixing this, but the current way to get the other endings is to watch the credits fully. That doesn't mean that you can't skip the credits - you can and it still works, and you should be able to get the other endings.
2.) I'll take note of that! Oliver's message isn't supposed to be like that, actually. t's supposed to be something else if you beat Claire up. But it IS intentional for you to not interact with Claire after that, atleast until Thursday.
3.) Will also take note of that...probably just cause I misspelt something
4.) Not really - each character has a somewhat different storyline, but the main thing is being friends with them all in all
5.) Actually, all of the endings are available. There is one secret ending called Python's Ending, which requires you to unlock the oc route. See the answer to question number 1 to see how!
Thank you for enjoying my game! I know it's got some bugs despite the bug testing, but it's all I got. Make sure to check the files of the game for extra content!