Hi. I have 4 tourist rentals all connected to the same wifi network. I have set up 4 Era 100’s using this network. At the moment, if one guest uses the Era 100 in their rental, the music is also played in the other rental properties. Clearly my other guests do not want to hear each others music! If I disable the wifi on each speaker, can the guests still play music via Bluetooth only? Or is wifi mandatory?