I think your 841n is quite an old device, maybe you can check the hardware version. As for as I know, router for home use has restrict the forward rules to its own lan only, for the consideration of...

i think you can find fw in this link: https://www.tp-link.com/ar/download/TL-WR841N_V13.html#Firmware

enable guest network, then you can config it

c50 support fb wifi, it will be the choice

emmm,,,Nano station loco M2 only support 11n 2.4G...

try access control, similar as mac filtering