So do it.
Why? If you must, and you insist on suggestions, I'd play something unobjectionable, classical, light and relaxing, such as Vivaldi's "Four Seasons". All it would take to change it to something more suitable (once you know what is more suitable) would be the click of a button.
That's why I suggested asking them when they book their session.
Nobody here can help you with this one. You have them in front of you, and only you can judge.
It's down to your own social skills.
Again, this is why I suggested asking them when they book their session.