Calendars 5 allows syncing with one Google account. But when using the built-in iPad/iPhone calendar app, you can connect other Google accounts to Calendars 5.
To connect to another Google account:
1. Launch iOS Settings app .
2. Go to Passwords & Accounts and tap Add Account. If you're using iOS 10.3.3 or earlier, go to Settings > Mail, Contacts, Calendars > Accounts and tap Add Account.
3. Select Google and sign in with your Google account credentials.
4. Make sure that Calendars toggle is enabled in the account settings.
5. Launch Calendars 5 and tap 
6. Then tap and go to Local Calendars settings menu and make sure that the toggle is enabled there.
7. Turn on Google Calendar toggle if you want to sync your main Google account through the local iOS calendar.
Note: When creating new events in Calendars 5 please check if the correct calendar is selected for the event.
