I would like to set up 3 XBee devices in API mode, one coordinator, two nodes. The coordinator will send payloads to either one of the nodes and address the XBee frames accordingly. The nodes will send messages only to the coordinator (never to each other).
Is it possible for the serial output of the node modules to trim off all API header/frame/checksum info before passing down data to the serial port (the device they are connected does not understand XBee API frame data). Likewise is it possible for the node modules to automatically add the relevant header/frame/checksum data when sending to the coordinator, again the device connected to the XBee serial port doesn't understand XBee frames so doesn't know how to add the frame data, only the payload.
I have complete control over the software at the coordinator end, so can manage the XBee frame data in my code there.
Yes, it's possible to run the non-coordinator devices in "AT mode" or "Transparent Serial" mode. It's also referred to as "Serial Cable Replacement Mode" because you can replace a serial cable with paired modules.
Configure DH and DL on the non-coordinators as 0 to automatically send serial data to the coordinator.
You can use Transmit API frames on the coordinator to address target nodes, and they will just send the payload out on the serial port.
You can even configure the modules with different baud rates.