While you can sometime hook up multiple Bluetooth things at once, I am not so sure it would work correctly with different speakers. Most phones don't come with multiple Bluetooth connection ability. Also, since the sounds are set to go to one place. Headphones, phone's speaker, attached speakers, etc., I do not think you would get it to play through multiple Bluetooth ones. At least not just using your phone alone.
That said, I know there are some apps out there that 'try' to make this work. From what I have seen it is kind of hit or miss with these. The other option would be if you had a hub that you could hook all the speakers to and then that connects to the phone via Bluetooth.