Can't see family sharing invitation on iPad mini
Confirm that your device is running the version of iOS that you think that it is under Settings > General

It might help to associate devices with that Apple ID, or at least log in to iTunes with the Apple ID to make sure that everything about the Apple ID works
http://support.apple.com/en-us/HT204074

You can also get to the invitation from Settings > iCloud > Family Sharing

here is info from the start
http://www.iphonehacks.com/2014/09/setup-family-sharing-iphone-ipad-ios-8.html

I was able to resolve all of my issues.