Can‘t setup an iPad or Apple TV as Home Hub
Try using the same Apple ID.

Make sure you follow all the steps in this article:


  
  Set up two-factor authentication for your Apple ID. On your iOS device, go to Settings > [your name] > iCloud and make sure that
  iCloud Keychain is turned on.
  On your Apple TV, go to Settings > Accounts and make sure that you're signed in to iCloud with the same Apple ID as your iOS device.
  After you sign in to iCloud, your Apple TV automatically sets itself up as a home hub.   To see if your Apple TV is connected as a
  home hub, go to Settings on your Apple TV. Then go to Accounts >
  iCloud and look under HomeKit.