You are right. It just works in router mode. In AP mode, to access internet, you have to check the option, ” Allow Guest to Access My Local Network”. http://www.tp-link.com/en/faq-519.html

Hardware version and firmware version of your W8951ND? MAC and iPad are both connected to Wi-Fi of W8951ND? Can you ping IP address of your iPad on your MAC successfully?

I cannot agree with you more. :o

Can you login web interface of W8968 on your laptop? On mobile and other devices, try to forget the network and reconnect with the password. If it doesn't work, you can reset and reconfigure your...

On web interface of WPA271, you can change SSID and secure Wi-Fi the same as your main router. Fix different channels for the router and powerline extender.

Did you refer to the guidance as below? If you tried pair correctly but cannot make them work, try to rename all of them with utility. http://www.tp-link.com/en/faq-258.html