Hey there.
The first issue with this is, that on every computer a specific port can only be bound by one application at a time.
With this line you’re choosing Port 12000 to be bound by your sketch and therefor the first instance you run is blocking that port for everyone else.
So either you go with a single server only and all the other sketches only send data to it or you will need to make each application have its own port.
This line determines where your data is sent to so it is fine to have this on multiple sketches: