As the girls get older they tend to increase their synchronization greatly, and it makes capturing artistic moments like this a lot easier. I also enjoy how good lighting by the stage crew can make this red/green one moment and red/white the next. So you might get a chance to have two or three versions of a frame provided for you mere seconds apart. One will usually work better for your mission of making than another.
If you can shoot your photos at the rehearsal I highly encourage you take advantage of the opportunity. It lets you just take in the moment as designed on the big night and does not bother other guests enjoying the show.