Did you choose the correct time zone?

yes, you can buy a third extender to add it into the powerline network. you can have a look at this instruction. https://www.tp-link.com/us/faq-1615.html

better to email tp-link support directly with your suggestion.

[FONT=times new roman]go to DHCP client list to check whether Chromecast obtain IP address. If there is, record the MAC address of Chromecast and go to wireless->wireless statistics to confirm. If...

try to check the IPV4 default gateway on your computer. use that ip to login the web page of the router. Note: make sure you do connect to the network of TL-WR841N.

If your model is TL-WR941N, you can try the firmware of TL-WR941ND. Note:make sure the hardware version should be same. For example, your current hardware is V2/V3, you also need to update the V2/V3...