When I login using vncviewer to vnc server it doesn't give me a user name in the login prompt, just a password. If I enter the password it won't log me in. I thought it might have a default username of admin and so only wanted a password, but no luck.
Whether VNC login requires a user name is determined by VNC server. Please check the authentication method set by your VNC server. Different VNC servers have different authentication methods. For example, if you select UNIX password, you must enter the UNIX user name and password. If you select VNC password, you do not need to enter the user name, because the VNC password authentication method does not need to verify the user name
When using VNC Viewer on Mac to Mac, shut off "VNC viewers may control screen with password:" in the Sharing > Remote Management. Delete the computer in the VNC Viewer app and Quit VNC Viewer. Start VNC Viewer and add the computer again and you should be able to add username and password of an account on the remote computer.