so one transmitter and many receivers. presumably no issue with transmitting in both directions
i have a model RR signaling system that has multiple nodes that need to share information. It uses Wifi. It sends broadcast UDP messages.
a typical msg indicates the status of a block, for example that block 101 is occupied
blk 101 1
the message is received by all nodes (slaves in your case) and they either use or ignore the information
you can do similar, sending a message to control a relay, by ID and the receiver will either process the request if it handles a relay with that ID