In the module 8 unit 4 of Learn ESP32 with Arduino IDE, the example shows the same message_struct is transmitted by all the slaves with the id identifying which slave the message is from. Can each slave send a different message_struct?
The data structure must be the same of the receiver. So, yes, all boards need to send the same data structure. But, of course, they can send different values inside the structure.
I hope this answers your question.