XBee Series 1 radios are generally used to replace wired serial connections, but with some easy modifications to the setup, they can be used to form a wireless network and communicate messages to a group of radios.
To accomplish this, all we have to do is modify the destination address and source address of the XBees using the XCTU tool, which can be downloaded from Digi here: https://www.digi.com/resources/documentation/digidocs/90001526/tasks/t_download_and_install_xctu.htm
To get the radios to communicate in a group, the destination address and source address should be the same, so that all the XBees send their messages to the same address, and they all receive the messages sent to that address.
Changing this with XCTU tool is as easy as modifying the values for the Destination Address Low to be the same as the 16-bit Source Address. I chose to have both be 0, but they can really be any number you want, as long as it fits under the size limit required by XCTU. To write the setting onto the XBee module, either press the pencil at the top of the settings to write all the settings at once, or press the smaller pencil button to the right of each entry to update individual entries.
After writing the settings to the module, it’s ready to communicate as part of the group!