Minecraft – How to use testfor to testfor players nearby

Two things:

• first you have two conflicting rules in your port forwarding rules, you are telling to forward port 25565 either to 192.168.0.1 either to your machine 192.168.0.104, you need just the latter one
• if your brother computer is inside the same network of your laptop then you don't need to open any port on the router (unless you want to allow people from outside to connect to the server) and you have to specify your local IP address (192.168.1.104) when trying to connect.

Of course any client from outside your network should try to connect to your external IP (the one shown in the port checker page).

There is this one character (I don't know what it is yet, either), that sometimes, somehow, makes its way into commands. Try going to the beginning of your /testfor command, and holding -> until you reach the end. There may be a spot where your cursor stops moving, and there should be a zero-width invisible character there. It shows up in regular editing software, I always check if my commands aren't working.