Deleting user documents

I'm creating a program that has data in a database connected to a user. In the future, this data will possibly be shared with other users (which will mean that multiple users will be given read and or edit permissions on documents).

How do I go about correctly deleting documents relating to the original creator, should there be an attribute in the documents that correlates to the ID of the original creator, so that when a user deletes their account, I can filter through all documents that specific user can access and delete them?

I essentially want to future proof so that I'm not deleting documents which a user has been added to, not necessarily created.

This is sort of two questions in one:

1. How do I delete documents relating to a specific user before I delete their account? (Is there a function for it)
2. How do I do it if multiple people have read / edit document permissions?

Sorry if this is confusing, if you don't understand anything just let me know and I'll try and explain it better.