@Izak > I'd suspect that the issue is with the D-LINK you're using to network them. If it's a router, sometimes the data between units can be blocked if any kind of traffic management or filtering is enabled. The best hardware to use is a network switch.
To troubleshoot this, connect a single CDJ directly to the computer - if it appears, the unit and cable are fine. If not, then there are other issues to consider.