Android calendar entries not synced/displayed on iPad

I have an iMac, iPad Air 2 and a Samsung Note 4 Android phone. I am trying to ensure all calendar entries are displayed on all devices no matter on which device it is first entered.

So far I can sync all entries entered via the iMac and the iPad with my Android phone via a specific android app.

I can sync any entry made on the android stock calendar with the iMac, having followed the process required. The event appears on the iMac calendar as a Google entry as Google is the calendar which I added under Calendar>Preferences>Accounts - add account.

So far so good

When I open my iPad calendar the android entered event does not appear even though it is on the iCloud calendar (albeit as a Google calendar entry). The only way I seem to able to get it to appear on the iPad is to change the descriptor for the event from Google to iCloud.

I have tried to add a Google account on the iPad as I did for the iMac process, but it will not add itself. I suspect this may be because I do not have a Google Mail account, which probably requires a separate user name and password (though I do have a Google account). I should add I do not want a Google Mail account. It is odd, however, that the Google entry is accepted by the iMac, but not by the iPad.

I have tried a number of possible solution from the web such as deleting accounts, switching devices off and on, but I suspect the answer may be more complex.

Any thoughts, comments or solution very welcome!