I see no requirement for frequency hopping in what you've described. You just need to set up a communication protocol between your slaves and master so that you guarantee packet delivery when collisions occur, which is to say that any time a slave sends a message it should keep retransmitting until it receives a response from the master. An XBee, for example, can do this automatically.
As to what device to recommend depends on the transmission distance and how much data is being sent. And how much money you have 