Thanks for your reply, Vijaya! That is good information to know.
I don't think we (my mom and I) would mind if they pass up our photos. I was just thinking that if they do want to use our expert's photos, that would be a nice thing to look forward to. Our expert was really helpful and pleasant to work with, and I would feel good if he got a photo payment out of it. His photos are of wildfires in specific locations, so they would probably be hard to get elsewhere.
For myself, I see the photos more as a way to help the article get into print, not a money source. But what you said about making an illustration from a submitted photo bothers me on a kind of theoretical level. If I understand things correctly, making a drawing or painting from a photo is considered making a "derivative work," the same as making a translation of someone's words. Both are protected by copyright, so they should not be doing that without your permission. I guess it would be okay to look at the photo as a way of thinking about the proportions or textures of the real object, and then use that abstract knowledge to make an original drawing, but the photo should be sent back first.