Google Calendar subscription shared with iCloud
You can not sync a Google calendar and an iCloud calendar out of the box. (Google and Apple both seem to avoid making it possible, probably because they both try to pull users onto their side.)

However:


All Apple devices can use and sync with Google calendars additional to iCloud calendars (I use it a lot with >10 Google calendars from >5 different users)
I saw some syncing tools that keep iCloud and Google calendars in sync, but a) they have to be always running somewhere and b) they are usually hacky and unstable.


You can Google both; I recommend 1.