You don't need a router, you need an Access Point.
So, either a standalone Access Point, or a router with WiFi where you can disable the router part in the settings.
Then, if you just use the same WiFi name and password it should look like one big WiFi to all devices.
And if you have a hardwired ethernet cable, of course you use that instead of Powerline, it's going to be way faster and way more stable.
You don't need a router, you need an Access Point.
So, either a standalone Access Point, or a router with WiFi where you can disable the router part in the settings.
Then, if you just use the same WiFi name and password it should look like one big WiFi to all devices.
And if you have a hardwired ethernet cable, of course you use that instead of Powerline, it's going to be way faster and way more stable.