Comunication Xbee S1 Coordinator to End Device
Choose a python XBee library, and use it to send a "Broadcast Message", which means it will go to all the end devices.
A Broadcast message is addressed like so:


  The 64-bit destination address should be set to 0x000000000000FFFF for
  a broadcast transmission (to all devices). The coordinator can be
  addressed by either setting the 64-bit address to all 0x00s and the
  16-bit address to 0xFFFE, OR by setting the 64-bit address to the
  coordinator's 64-bit address and the 16-bit address to 0x0000. For all
  other transmissions, setting the 16-bit address to the correct 16-bit
  address can help improve performance when transmitting to multiple
  destinations. If a 16-bit address is not known, this field should be
  set to 0xFFFE (unknown).


If you don't want to use a Library, you can build the packet yourself using the Reference for your version of XBee (eg https://www.digi.com/resources/documentation/digidocs/pdfs/90000976.pdf) and look at the section for "ZigBee Transmit Request  Frame type: 0x10".  Send data matching that format and it should work.

But i'd recommend using the library.