Sorry I have problem with understanding your last post. Are you need Portuguese firmware for WR841N, right?

I'm not sure of my advice for 100% but you can test it. Firstly you have to change web management port on Archer C9 for example 85. Advanced->System Tools->Administration and Remote Managment.

SOHO TP-Link doesn't have roaming feature and sometimes have problem with choose good access point. http://www.tp-link.com.pl/faq-592.html http://www.tp-link.com.pl/faq-593.html In that configuration...

Wake on LAN by TP-link by devices - http://www.tp-link.com.pl/faq-922.html

Are you asking about tether app password or router password?

You have to check second point of your speech "AP Isolation" on the WR740N.