Sorry, reading through the threads quickly it seemed as though you only had two computers on your network.
You can continue adding unauthorized MAC addresses to the block list, or gather a list of MAC addresses that are known to be good, and then add them to the allow list on your router.
I guess I don't know what kind of environment you're working in, whether it be a work / home / school /etc. environment and I don't know what type of routers / servers you are running.
If you had a Windows DHCP controller, you could easily see the authorized computers on your network, and pull the MAC addresses from there. If your only DHCP server is your router, then you have to rely on it to provide you with the relevant information.