Multiple xbees on same network
My answer here may help: The appropriate code (Arduino) of Xbee

Once you have one master and one slave like in that answer, repeat the slave configuration steps for the second slave. Then:


To send from slave to master, just send the data. 
To send from master
to a slave, set the master's DH and DL to the slave's SH and SL
respectively, then exit command mode (ATCN) and send the data. To
send to the second slave, do the same but using the second slave's
SH/SL.


Note that when you use AT mode and the slaves send simultaneously, the bytes may become mixed at the master. E.g Slave1 sends "hello", Slave2 sends "there", master gets something like "hethelrloe" (painful own experience. :) At some point you will end up needing API mode, but AT mode is a very good, simple, way to start.

The tools and tutorials I found useful on XBee, I gathered them here: 
http://erion.elmasllari.com/2012/06/in-the-trenches-with-xbee-resources-and-tips/

Good luck!