I'd like to add a calendar to my account, to share with friends.

Not sure how I did it, but I set up an account for my wife so she could have her own calendar. Now, I'd like to share calendars with some friends, so do I need to create a new account for each or just share one? They need to be able to edit the calendar. Makes it easy for us to share dates and not have to email back-and-forth to get it done.

Thanks!