AirServer allows you to connect multiple devices simultaneously. To mirror multiple devices, you just have to switch on screen mirroring on each device and select AirServer as your destination, as you would normally.
As each new device connects, AirServer will automatically split the screen to accommodate for each new device. Airserver will automatically display them and choose the most optimal usage of the screen.
Please note, the number of devices that you can simultaneously stream to a computer would depend on the strength and speed of your network and computer. There is no exact way to measure the needed bandwidth to support multiple connections, as it would vary depending on the content being streamed from the devices.