When a server process tries to acquire a port that has already been acquired by a second process I'm assuming it fails? If so, can the server backoff and retry to find the next port that is available? This might help deal with contention when multiple processes are detecting the same port as available.
Alternatively, you could pass in a static port number as a parameter to your
ServerLaunchParameters. Since you have a fixed number of processes are going to launch, each could read a different unique parameter that it can use to as the port number it will try to acquire, completely avoiding contention.