Hi,
I've got the Echo and two dots around the house, If you ask a question then only the nearest one to you will answer. If you ask Alexa to play music then that will come out of the nearest dot or echo that heard you and not out of the others. If you use a Skill then that would apply to any dot or echo. So you may have a few home automation switches to turn on Garden lights, any dot or echo on the same account will respond to that. Each dot can be connected to a Bluetooth speaker but your dots can't share a Bluetooth speaker they each connect separately.
Jez.