Allow friends to edit your events
Your friends will be able to edit calendars that you've specifically shared with them. First, you'll need to share your calendars with your friends. Once you've invited your friends to share your calendars, select the "Make changes to events" permission from the drop-down menu in the "Share with specific people" section.
If you'd like your friends to be able to edit the calendar's sharing options as well, just select "Make changes AND manage sharing."