In the callback, what you need is
"address = xbee_message.remote_device.get_64bit_addr()"
if you want to get the address of the sender.
And if you want to send back an AT command to the sender, for example, to set a pin to digital output high, use the local Xbee to send a RemoteATCommandPacket to the local.
Here is an example: (set D4 of remoted Xbee to high)
#make an AT Command Packet
ATcommand = RemoteATCommandPacket(1,address_of_remoted_Xbee,XBee16BitAddress.from_hex_string("FFFE"),
#then send the packet from local_Xbee