Whenever the canons fire, the dancers raise their arms and jump around to indicate the canons firing. The lights turn yellow, too. This could be because whenever something explodes, it usually goes up, or just explodes with a lot of force.
The characters, with the sisters in the front, look out into the crowd as if looking at the harbor. Their voices get louder as they say the last 'when they surround our troops' to indicate that the British are close and that this means danger. The lights are blue, not a good joyful-feeling color, so it shows that trouble is in the air.
I hope this helps! I'm not all that good in theatrical stuff, but I was just looking at the video. Good luck!
