Not sure what you mean when you mean the the Wi-Fi originates through the desktop. Is the desktop connected to the router (whether wired or wireless)? For the machines to talk to each other, they all have to be on the same network i.e. connected to the common router.
This might be a good time for you to learn some basic IP networking, just so that you can verify that the machines can all talk to each other at the basic level. On each PC, open a Command Prompt (prob. under Accessories) and type the following:
ipconfig
It should return a couple of lines including an "IP Address" with 4 digits. The details from all the PCs should be nearly identical, with only the last digit (or two) of the IP address being different. To verify that one PC can see another PC, type:
ping <ip address>
using the IP address of the other machine.
(When someone asks you "can you see the other machine", this is the place to start. If ping doesn't work, nothing else will work, so you must fix the basic IP networking before worrying about any "high level" functions like file sharing or printing. It's as fundamental as the wings on a plane.)
If this all works out, then you should be able to go to "Network Neighbourhood" and see each machine from the others, but depending on the Windows version, you may need to enable File Sharing on one or more of them. Windows now has a "firewall" that makes machines invisible (as a security measure) and enabling File Sharing or Printer Sharing as required "opens it up" so you can see the other PC.