I am trying to give SSH access to some external people via a single box. If they ssh to that box they will be automatically redirected to the target box. Is this possible?
Not enough detail.
However I presume that the target box varies from person to person, otherwise you could do it with a firewall rule or a redirector to the target box. If so, you would need captive ssh logins on the intermediate box that would run another ssh to the target box.
If you only have a few machines to manage, use one port forward for each target machine and tell them which port to use.