The problem is that adduser uses steamids, and in LAN all steamids are STEAM_ID_LAN. You can add the users based on IP, or name, but to do so you will need to actually edit the data/ULib/users.txt file manually. If you are going to be playing with other people who you do not want to be able to get superadmin access then I recommend using a password for his account. Also, if you are going by IP then you should set his computer up with a static IP address so you don't have to change the ip in users.txt every time his ip changes.
