You can join additional adapters into a running PLC network either by pressing buttons in a certain sequence, or by entering the device ID code in the tpPLC utility "Add Device" function. Please read...

... and your question is?

@tonduma First of all, join them all into one PLC network. Then, for WiFi equipment that is not Mesh capable, manually put all the WiFi APs onto the same SSID and passkey, but on different channels....

I used the NVM file from this other thread's first page and the PIB from the latest official firmware package. Update procedure was with latest tpPLC software on Windows 10, with the PLC connected...

Update: The other adapter from the same pair updated successfully as well.

There is a recovery tool available from tp-link.