Family Sharing - including all calendars...?!

I am generally happy with the option to share purchases across members of my Apple iCloud Family. What I realized today though was that apparently they can all also see each and every calendar of mine listed in their Calendar apps.

That seems really odd, and even more unnecessary - why would I burden them with every little appointment I make.... How do I turn this sharing off? Apart from hiding those calendars on each individual iDevices' Calendar app, which is easy to reverse (should they want to)?

Best regards, Ole