Planning the Band Performance Film Shoot

I have recently contacted the cast for the band performance, and asked them whether or not they are available on Tuesday 6th December, and Tuesday 13th December from 3.30pm until 5.00pm. They have all replied that they are available for this, therefore I am planning to film the band performance parts of my music video on these dates. As there are four actors for this, it is possible that at least one of them may have something else come up meaning they will not be able to film on these dates. If this is the case, I will have to rearrange to another Tuesday; as this is the only day of the week in which all of them are available after school. I will need to gain permission from the drama/music teachers to use the instruments as props, and access the drama hall on these dates before I can confirm to my cast that the film shoots are taking place.