How to create a bluetooth module that is both a master and slave?
It all comes down to what different micros support. Take a look at the PSOC4, which comes in BLE and Bluetooth classic. The choice comes down to whether or not you are trying to get audio back and forth between the speakers or just a little general info. For audio, do not use BLE as the throughput will not be high enough for you. Though on that same not Bluetooth classic may have some noticeable latency.

That said, the part has a very nice command for you which allows you to switch back and forth between slave and master, so you should be able to accomplish what you need based on switching back and forth on a timer or when a given flag is set. Getting smart on the timing will allow you to bypass the need for being in both at once. Hopefully this is what you were looking for.