How to prioritize the receive channel of the endpoint?

We are working in a three XBee’s network (1 coordinator and 2 endpoints).
We are sending cyclic messages (100 bytes in 57600) from the endpoints and
we receive it in the coordinator (which is our ground station). If the
coordinator will try to send a message, during that time it fails most of
the time, which will cause our system to get into timeout state as it is
waiting for too much time for a response from the coordinator (ground

Have you read through the broadcast function in the product manual yet? Have you also read through the streaming limits?

Are you aware that Zigbee is a slow or low data rate protocol? That is to say, it is only designed to send small (Sub 100 byte packets) once every so often (a few seconds to several min later).