RAK LX200V20 should have MII interface,so if you need ethernet port, you need add external PHY chip. Of course, you can buy our EVK to connect to your MCU through ethernet port easily.But i think this is in evaluation stage. Pls refer to our module documents via:http://www.rakwireless.com/en/download
For your use case, it can be realized. One module connect to router, the other connect to your boards. It can communicate via powerline.