Add true multi-user functionality to the app

I want to be able to login and add additional users' email addresses who can manage our system via the app. I'd like to have different levels of functionality - admin can do all functions, member can operate the system, limited duration member can operate the system only on authorized days (e.g., weekly house cleaner can operate on Tuesdays or house sitter can operate for ten days, or dog walker can operate between 8am and noon).