My work uses Exchange, so I use Fantastical on mobile and Apple Calendar/iCal on my Mac to display both my work calendar (in Exchange) and my personal Google Calendar.
I have two calendars in my Google Calendar that were shared with my Google Calendar account by their owner (both are also Google Calendar). I also have a variety of subscribed public calendars. For some reason, when I add a Google account both to iCal and Fantastical, I see my subscribed public calendars but not the private calendars.
I also went to see if I could manually add the .ical, but I don't see a link for the .ical in the Google Calendar web interface.
I suppose I could ask the calendar owner to share their Google Calendar with my work account, but it seems like there should be another way? Given that it's been shared with my Google Calendar account and that I have logged into Google Calendar.