I bought Minecraft for ps4 on my account. How can it be on everybody's account?

That's how it should work, every user on the console can access the games you by, they just have their own save files and game progress
that passcode is just for parental control settings and to block anyone from using the browser from your account, it doesn't lock anything

here is what you need to do - buy her a ps4 or just say I want to use my ps4, you can play later
Now, if its not your ps4 but one your parents bought the family you just need to act mature and learn to share, tell your sister she gets to play for half the day then you play the rest of the day or have your parents make a schedule