Based off of your question, I am presuming that you are using a Zigbee XBee module. Simply set the Base module as your Coordinator (CE 1), the DL and DH to the broadcast address. MP is filled in by the Coordinator automatically and is not settable by you.
The other two nodes would have their DL and DH set to the Coordinator SL and SH values.
In this configuration, the Coordinator will send to all nodes. The remote nodes will send their data to the Coordinator.
Digi RF Support