Can multiple bluetooth speakers be connected from iMac bluetooth?

Hello Darker,

Yes, that is easy to do! All you have to do is open the Apple Audio MIDI setup in your utilities folder then click the plus sign at the bottom left of the window to create a multi-output device, select your internal speakers and your bluetooth speaker (this needs to be pair with your computer) you should see the Multi-Output device in the right side window. Go into your system preferences>sound then select that Multi-Output device as your output source. You should hear sound in both devices.

Thank-you daapple

It is exactly what I was looking for.

Is it possible to use an iPhone as the source instead of the MacBook?

No it is not possible unless you use a 3rd party app or a sound bar