How can we set up wireshark to display all Devices connected to our Netork (Router)

Look into 'monitor port', or 'SPAN' for instance.

Wireshark is no network mapping tool in itself, but you can use it to capture network packets and analyze them or create statistics on what devices talk to what other devices. So if you're looking for some kind of software that will scan you network and tell you about all the devices it has found Wireshark is not that much for you.

What you can do is hook up Wireshark to you router and have it "copy" all network packets (inbound and outbound) from all other ports to the port Wireshark is connected at. That is what Jaap meant when he said you might have a look into monitor ports A.K.A SPAN ports. This kind of functionality depends on the abilities of your router to do such a thing; not all routers have it or can provide monitor sessions for all ports.

All in all I would advise you to give us more details of your situation/requirements and you might get a much better answer ;-)

If you want to do this without modifying your network devices (e.g. switches), nmap might be a better tool for this project. It will scan entire subnets and present a list of "discovered" hosts and (if open) the service ports open on each host.

You can find both command-line and GUI versions of nmap at http://nmap.org/.

WARNING: This is an ACTIVE port scanner, and it WILL trigger many (if not most) intrusion detection systems. Be sure you have permission to run it against the networks in question before doing so.