I found an easy fix, and often neglected step, in the how-to section of the Google Calendar support page. This step ensures that the calendar you’re looking at on your iphone has the latest, and most current events, even if you’re syncing multiple calendars from members of your family using Google calendars, which they share with you.
First, if you haven’t already done this, add your Google account to your iPhone. You can add multiple Google email accounts. To do this, simply go to Go to Settings, then open Mail/Contacts/Calendars. Select Add Account and Gmail. Add your Google account information and a description of the calendar, and ensure that the Calendar option is switched on. Continue to add Google calendars individually as needed.
(If you are already sharing multiple calendars on Google, you do not need to add each Google account to have all of those calendar events appear on your iPhone calendar. Those events will automatically appear on your calendar once your iPhone/iPad is synced, just like they do when you are on a computer looking at your Google calendar. For more on how to do this, read here. )
Once your Google account(s) are added, ensure that the calendar toggle switch is “on.”
Now, here’s the GOLDEN step — the one that always gets missed in the how-to sync your iPhone calendar posts.
Open this webpage: www.google.com/calendar/iphoneselect
There, you will see all the Google accounts and shared Google calenders you have access to. Simply check the ones you would like to appear on your iPhone.