Is the sender COM15 is sending hex data, but the receiver is reading binary data?
Hex data IS binary data.
Serial.write(&myNumber.B,4);
//Serial.print(myNumber.UL, HEX);if (Serial.available()) myNumber.B[x++] = Serial.read();
} Serial.print(myNumber.UL, HEX);
Using the same port to send data to a serial port monitor AND to the XBee is going to cause frustration.
How are the XBees connected to the Arduinos? If you are using shields that have an option to select which pins the XBee is connected to, or you are using wires to connect the XBee TX/RX pins to the Arduino, using something other than the hardware serial pins to talk to the XBee and using the hardware serial pins to talk to the PC would be much easier.