iCamSource will work fine with multiple cameras, you just need to run one instance of iCamSource for each camera.
We have heard reports of people having issues running multiple cameras on a hub, but that's more of a hardware issue. If your computer and your hub can handle 4 cameras simultaneously, then iCamSource should work fine with it.
One thing to keep in mind is that the CPU resources required will scale up with the number of cameras. If your computer uses a lot of CPU to run one instance of iCamSource, then there's a good chance it won't be able to handle 4 of them simultaneously.
