I have not tried this. From my reading, the Chromecast Video and the Chromecast Audio are independent products and you can only broadcast to one or the other.
However, if you Google your question (such as "can I broadcast to multiple chromecast video"), you will find tips on how to broadcast to multiple Chromecast video products. This might work as a solution.
Chromecast audio can broadcast to multiple Chromecast audio units but I don't think this will solve your problem since you desire an audio / video presentation.