Have you looked into the BluetoothAdapter
Android class? You set up one device as a server and the other as a client. It may be possible (although I haven't looked into it myself) to connect multiple clients to the server.
I have had success connecting a BlueTooth audio device to a phone while it also had this BluetoothAdapter
connection to another phone, but I haven't tried with three phones. At least this tells me that the Bluetooth radio can tolerate multiple simultaneous connections :)