Hello @Robby9876
If you set them up first relatively close to the primary/main unit via WiFi (as you have planned), you should then be able to connect one of the secondaries back to the primary's LAN Ethernet port using either one of the ports on the secondary (just pick one and stick with it, though). No other configuration is required. I would recommend testing this one step at a time, perhaps using a shorter Ethernet cable first and then connecting the longer one. I would also consider picking up at least one inexpensive, unmanaged Ethernet switch. Connect that to the primary's LAN Ethernet port and then connect the long Ethernet cable to the switch. If the other end of the cable is in another building, put another inexpensive Ethernet switch on the other end of that cable just for increased electrical isolation (replacing switches is less expensive than replacing access points/routers). This can also help to provide more Ethernet ports to connect other devices in your home (TVs in particular benefit from this, but gaming consoles, computers, printers, etc. will as well).
