Repeater or Universal Repeater? To work with TD-W8951ND, you should use Universal Repeater mode. http://www.tp-link.com/en/article/?faqid=250

Follow this. http://www.tp-link.com/en/article/?faqid=227

Hi Frank, can you access internet if clients connected to LAN ports of Archer C7? Try to modify some wireless setttings, like channel.

What's the WAN IP address for WAN1 and WAN2? They shoud be public IP addresses.

http://www.tp-link.com/en/article/?faqid=572

Are you able to connect some other wireless clients to the Wi-Fi Hotspot created by iPhone 5S? Is it stable enough? Did you try to follow this instruction? http://www.tp-link.com/en/article/?faqid=679