In windows start the File and printer sharing wizard when all the PCs are connected to the router.
Remember to Share the Printer.
Then get to each connected device and and either maps the shared resources through it or use it's wizard to search for shared resources on the LAN.
The only problem is going to be the connection to the net, if any of these devices is not securely configured within the LAN then the resources are going to be open to people who join the network either over the air or via the internet.
Be sure to enable firewalls and be sure to dedicate required ports within the firewall for LAN connections and sharing of resources.
It's not as difficult as it sounds but takes a little time and patience.