Hi,there
Thanks for your feedback,for the xbee shield while is connect to the D11,D12,that is compatible for the mega,the mega message:
Not all pins on the Mega and Mega 2560 support change interrupts,
so only the following can be used for RX: 10, 11, 12, 13, 50, 51, 52, 53, 62, 63, 64, 65, 66, 67, 68, 69
if we use the D2 to D7,it will not compatible for the mega.
For the NFC and bluetooth together,you can use the Bees Shield.
Link:http://www.seeedstudio.com/depot/bees-shield-p-672.html?cPath=109