Apart from any other problems that you may have I didn't bother to look beyond the fact that the code you posted has two setup() and loop() functions in it so I assume that it is not actually the code that you are using.
That does not make any sense. What you have done is to tell the Serial monitor to append a Carriage Return to the text sent to the Arduino, but the code that you posted does not rely on the CR being present.
The principle will work for as many servos as the receiving device can support but whichever method you use bear in mind that the calls to the function will happen in a sequence and not all at the same time. It is up to the receiving device to interpret and act on the commands appropriately.