Rev. Marsh, I've had a more thorough think at this, hope these instructions are helpful:
So if you both have Google accounts, (easy way to tell, you have an email address ending in @gmail.com or @googlemail.com), you simply add those accounts to both phones. When adding your account to your wife's phone, tick only Calendar to be synchronised, and when adding her account to yours do the same. This will have two calendars on both phones. Adding events to the calendar on the phone or on the Google website should cause them to appear on both.
If you need to make a new Google account, a quick way to do so with Android is under Settings > Accounts > Add Account > Google > 'Or create a new account'
If you both have Google accounts, you do the following to add eachother's to your phone. This could also work with Microsoft Hotmail accounts, if you choose Microsoft instead of Google at each step.
First, on Android:
I'm looking at a Samsung Galaxy phone, but the steps should be similar for most.
With Android, go to Settings > Accounts > Add Account > Google
Then, type in the email address and password. Say no thanks to any payment info. (They've made enough already.)
You should be back in the Accounts screen. Press 'Google,' then the email address you just added, then uncheck everything apart from Calendar. This way you will only be getting her calendar and not App data, Contacts, etc.*
Then, for the iPhone:
My only iPhone is running iOS 6 (!) but I don't see why Apple would have changed the menu options.
Go to Settings > Mail, Contacts, Calendars > Add Account...
Choose 'Google Mail' and enter the username and password. Save this account then on the next screen check off everything except 'Calendars'. Tell the phone to keep local calendars if it asks you. Then press 'Save'.
There! With that, both your accounts should show on the other's phone.
*Otherwise, if you think it would be simpler and want only the one calendar for both phones, you could create a new Google account and only use it for the calendar and add this new account to both phones. You might find that option handier and less likely to have data conflicts. It's the same processes to add this one account to both phones.
I've added a few other options so you may decide what best matches your setup. If you need any more clarity with these steps or if something doesn't quite work, I'll still be here.
