My parent’s have their ONT inside a basement cabinet, where all the house ethernet cables terminate. One of those cables runs up to their office, where the main Wi-Fi router is located (Plume homepod provided by their ISP).
Could they setup their network similar to what’s shown in the diagram where the WAN and LAN traffic passes through the same ethernet cable? If so, are there any specific network settings that should be enabled to prevent any issues?
Technically you could through VLANs, but I would just put your router in the basement near the point of entry, and then put an Access Point where your current router is now.