It will likely scare them the first time as it’s new/unfamiliar, but they’ll begin to normalize it with repeated events (as long as there is no physical/situational aggressiveness toward them). Once they acclimate to the singing, they might still get a small jump scare if you begin abruptly belting out something, but as you continue the song they would likely relax back down recognizing it as not a danger. I find most pets will try to hide/runaway when they don’t like a sound, so indifference from a pet is akin to general acceptance of your presence imo.
Here’s wishing you a wonderful performance!
Go to Meow Wolf in Houston!!! It’s immersive art- so think art museum that you can touch the walls and interact with the artwork. Their experience in Houston is called Radio Tave. Give yourself a good amount of time to explore an wear comfortable clothing/shoes. Meow Wolf does attempt to make their art installations accessible for all sizes, ages, and abilities- so if you visit while on crutches, on a walker, or in a wheelchair, both you and your dad should still have an enjoyable time! Hope it all goes well!