Follow these steps if you would like multiple calendars from your D-E Google account to show up in the native iOS Calendar application on your iPhone or iPad. 

1. Add you d-e.org account to your device using the Microsoft Exchange setting per the directions here: Setting up Google Sync with your iOS device.
2. Select the calendars you want to access from your device using the directions here: Using Google Sync with iOS Calendar. 
1. Note that the link to the https://m.google.com/sync/settings/ requires the trailing slash.