TL;DR

• Set coworkers' calendars to be synchronizable on Apple Calendar in Sync Settings page. 
• For more details, please check official support page.

Introduction

If you are in a company that uses Google G Suite, it is common that the company uses Gmail, Google Drive, and Google Calendar as its email, cloud storage, and schedule systems. The Google services are easily available not only on Android, but also on iOS if you use Google official apps. However, if you are already using iOS default applications such as Mail and Apple Calendar, you need to integrate your account information with the default Apple apps. But unlike Mail app, the integration of your G Suite accounts on Apple Calendar is not intuitive. 

Here I simply introduce how to synchronize your Google G Suite Calendar with your Apple Calendar app on iOS. 

Key Understanding

Calendars appeared in 'My calendar' section and 'Birthday' section are automatically synchronized for iPhone/iPad/iCal as default, but calendars appeared in 'Other calendar' section are not automatically synchronized even if each calendar is set to be sharable. For more information, please refer See Google Calendar events on Apple Calendar in official support page.

Full Steps

You need to follow three steps:

1. Add other Google G Suite member's calendars to your calendar
2. Set their calendar to be synchronizable
3. Add your Google G Suite account to Apple Calendar

Note that the key step is second step. First step and third step are the same as usual.

Add other Google G Suite members' calendars to your calendar

Let's add your coworkers' calendar to your calendar.

1. Sign in and go to Google Calendar with your Google G Suite account on desktop.
2. On the left side, you can find 'My calendars' and 'Other calendars' section.  
3. Under the 'Other calendars' section title, you can find 'Add a coworker's calendar' input field. 
4. Type and add your coworker's name or email address to show his/her calendar to your calendar.
5. Now you can see the coworker's calendar name in the 'Other calendars' section and the coworker's calendar is synchronized in your calendar view. 

After the end of above steps, you can check the coworker's calendar in calendar view on browsers, the official Google Calendar app for both of iOS and Android, and some other calendar apps except the official Apple Calendar app on iOS and Mac. 

Set their calendar to be synchronizable

As explained in the Key Understanding section, calendars shown in the 'Other calendars' section is not synchronized as a default setting. You need to explicitly choose what other calendars to be synchronized.

1. Go to Sync Settings page.
2. Check the coworkers' calendars you want to be shown in your Apple Calendar.
3. Select Save button.

Good, we are almost done. If you already add your Google G Suite account to your Apple Calendar app, you can find the coworkers' calendars in calendar list. If you don't yet add your Google G Suite account to Apple Calendar, let's go to the final step.

Add your Google G Suite account to Apple Calendar

This is the final step, adding your Google G Suite account to your Apple Calendar app.

iOS:

1. Open 'Settings - Calendar - Accounts' (Not Calendar app, but Settings!)
2. Choose 'Add Account'
3. Choose 'Google'
4. Sign in with your Google G Suite account.
5. Turn on 'Calendar' and other applications if you want.
6. Save

Mac:

1. Open Apple Calendar app on your Mac.
2. Choose 'Calendar - Add Account...' in the menu bar.
3. Choose 'Google'
4. Sign in with your Google G Suite account.
5. Turn on Calendar and other applications if you want.
6. Done

Everything Done. Now you can open the Calendar app and see the coworkers' calendar list when you touch 'Calendars' button in the bottom of the screen in iOS and in the left side panel in Mac.

Okay, everything done.

Additional Information

If you want to share your Google G Suite Calendar to external accounts (not Google G Suite accounts), you need to configure additional settings not explained in this post. Please refer to Managing Calendar for G Suite.