The generic code for the heart-to-heart project, swap 'hunter dozen' to your event name and swap the numbers associated with it (hunter_dozen_button_pressed_1,2,3...) to flash this to multiple particles

thislove.ino

/*****************************************************
 * Author: Greg Mankes
 * Date: 1/8/16
 * Description: This Program publishes and subscribes
 * to an event to a separate photon. When each Photon
 * receives the event, the board LED will light up. 
 * When a user presses a button, the photon will 
 * publish an event
 ****************************************************/

int boardLed = D7;
int pushButton = D6;
void myHandler(const char *, const char *);

void setup() {
  
  Particle.unsubscribe(); // unsubscribe from previous if any

  pinMode(boardLed,OUTPUT); // Our on-board LED is output
  
  pinMode(pushButton, INPUT);// Set up a pull up resistor push button at pin 

  // Here we are going to subscribe to your buddy's event using Spark.subscribe
  Particle.subscribe("hunter_dozen_button_pressed_1", myHandler, MY_DEVICES);
  // Subscribe will listen for the event buddy_unique_event_name and, when it finds it, will run myHandler()
  
  Serial.begin(9600);
}

void loop() {
  // This loop sends a publish when the beam is broken.
  if (digitalRead(pushButton) == LOW) {
        Particle.publish("hunter_dozen_button_pressed_2","pressed",PRIVATE);
        // publish this public event
        // rename your_unique_event_name with your actual unique event name. No spaces, 63 ASCII characters.
        delay(1000);
  }
  else {
        // publish that the button isn't pressed
        Particle.publish("hunter_dozen_button_pressed_2","notPressed",PRIVATE);
        delay(1000);
  }
}

// Now for the myHandler function, which is called when the cloud tells us that our buddy's event is published.
void myHandler(const char *event, const char *data)
{
  
  if(strcmp(data,"pressed")==0){
    digitalWrite(boardLed, HIGH);
  }
  else{
    digitalWrite(boardLed, LOW);
  }
  
}

This code has some flaws in it such that at the time, you needed to have a delay in publishing an event. This can be attributed to the documentation (due to spark's transition to particle) and may not be necessary anymore. Be sure to check the documentation.