Please don't take this the wrong way, as it is not intended to sound as it may. But over the years, Apple has done an impeccable job of trying to make the public/users understand that they should have separate Apple ID's for each person. They even created Family Sharing, which does a great job. I have teenagers now and since they were 6, they have had their own apple id's for their ipad and now iphone's. They want an app, music or book, etc, then they request it and the request comes to mine and my husband's phones to accept or deny. We can all share apps, music, books, etc and my parental controls prevent them from accessing those shared items that I may not want them having. I can see where they are on GPS as well. It makes alot of sense why you would need separate ID's when you think about it.
So, I'm not sure why anyone shares an apple id anymore. In my honest opinion, this is not really Apple's bug to fix - it's been documented and explained what everyone should do for years now with regards to apple id's. So I would go through the process mentioned above and reset the phone with a separate apple id for each person.