The sky hub is connected to the LAN port of the C7, right? What's the Ip address of your sky hub? Be careful about IP conflict.

If it fails at 40%, restart the router. Try a few times. It worked for me. Otherwise, contact tplink support

C60 v1 supports QoS too. It should be available via Tether. Are you using the latest tether app? Did you enable remote management on your router? If not, that's very strange.

You want to set the VR600v in router mode? Need to login to change its operation mode. If 192.168.1.1 brings up the Dlink page, then it's probably caused by IP conflict. Do not connect the AC1200...

Does the router have WAN IP address? Maybe it's about the DNS server. Change the router's DNS to 8.8.8.8

Are they showing up on the kasa app when you operate on local site? If not, you need to add them to the app. If you can operate them locally but not remotely, check whether remote control is enabled....