You can hook up multiple WiFi birdhouse camera to your home network. Each IP cameras works standalone. Technically there is no limited to the amount of the IP camera you can add to the network. You may need to evaluate the capacity of your home WiFi. Unlike the mobile phone, the IP nest box camera need to transmit the high definition through the WiFi router, the data traffic is much bigger than the web page surfacing.
There is no difference to hook up the second camera. You can use the exactly the same process to connect the new camera. You will have new camera listed in the iCSee app, and you can watch the camera one by one or 4 cameras in the same screen.
While you will the PC or Mac software, you will be able to view 16 cameras at the single screen, but it also depends on the CPU resource of the computer. It needs lots of CPU source to decoding such high amount of HD camera.