3 or more XBee in transparent mode

I’ve been using 2 XBee PRO 900s so far successfully (1 in UAV, 1 Ground Station) in transparent mode. I would like to set up a second UAV with an XBee PRO 900. I want all 3 XBees to Rx and Tx with each other. I anticipate to do this in transparent mode, I would do all the addressing in my software application while the XBees would broadcast to all other XBees. My question is, what would happen if the two UAV transmits data meant for the Ground Station at the same time. Understanding that “transparent mode” is like a serial cable, would the Ground Station receive both UAVs data orderly? Or would the Ground Station received a garbled mix of both UAV data which would need to be ignored / thrown out? Thanks in advanced.