ssh -L5900:192.168.2.3:5900 10.0.0.9

ssh -L<local-VNC-port>:<IP-of-G5>:<port-of-screensharing-at-G5> <IP-of-Mac-Mini>

Host g5
  User <username-for-Mac-Mini>
  HostName <hostname-of-Mac-Mini>
  ProxyCommand nohup ssh <hostname-of-G5> %h %p