Is there any instruction from your ISP about how to configure IPTV? Confirm it with your ISP. Provide a topology pls. Is the a set-up box in the network?

"Network Connection Status Inspect(NCSI) - Fail" may be caused by network congetion when you test it... No worries...as the network is working fine...

Follow the guide here to login its web interface and change wireless settings. http://www.tp-link.com/en/faq-398.html

The router room and flat room are in the same electrical meter? If so, you can buy a powerline extender kit like TL-WPA4220KIT. Connect the wired one to your router and wireless one in your room....

What's the rate between powerline adapters? Did you have a check on its utility? 11Mbps wifi went down to 9Mbs. Brilliant. My access speed is average 34Mps. As PA411KIT has no Wi-Fi function, are you...

What's the firmware version of WR941 and RE200? 5G/2.4G light on RE200 is red or green? Can you place RE200 closer to WR941 and have a test?