Good for eyes. Bad for photos.
Do they have a different pair? No? Just take them off.
Don’t wait until you’re editing pictures to say “Man, I wish I’d asked them to remove their glasses.” Better yet, ask before the shoot if anybody in the group uses transition lenses and have them bring a different pair. That way they don’t feel like ‘that guy/gal’ who’s wearing sunglasses when nobody else is. You can do some editing to make it less apparent, but it’s easier to address it up front.
Photography is all about the little things.