The SSID is the name of the wireless network, it is just a name to identify it. For file sharing across the network, all computers need to be in the same "Workgroup", which is the network's name within Microsoft Windows Networking.
For your four computers to see one another, they need to be in the *same* subnet. For example if some PCs have IP addresses in the 192.168.1.x range and others in 192.168.2.x with a subnet mask of 255.255.255.0 the two ranges cannot communicate. If you are able to change the subnet mask throughout the two networks (which is effectively what you have) to 255.255.0.0 they may then all see each other.