Basically, I want to disable multiple logins. The family laptop (not mine) has a problem with the x server -- at least it seems to be the x server. When two users are logged in simultaneously the x-server fails to start for the one who was logged in first. Having two users logged in seems to steal processor speed anyway. So I want to disable people from choosing 'switch user' over 'log out (username)' or 'shut down'.
There is a setting
You can change this setting by running