Ordinarily they don't do this however it seems a tactful way of saying they don't like their photos
At the moment they're just too plastic-looking for my tastes.
I agree with these sentiments, and I'd venture a guess that either one of them has some photo knowledge, or they have a friend that does, thus why they'd want the RAW files (to process their own way).
I'd offer to give them the RAW files. Highly unusual but so is your work.
The other option, if you're comfortable with it, is to take the meeting and see what they are looking for specifically. Maybe it's a few simple changes (backing off the highlights, less brushing, etc), and then offering to re-do them in that style. Don't let them sit their for the entire editing, but, give them a few other options for how the photos might be processed.
It could avoid a messy situation, while also not dealing with the awkwardness that would be them sitting in on your entire edit (which would take significantly longer).
Do you have your webpage? Are these a departure from your normal style? Cause that will matter too. If all your other stuff looks the same, I'd be less inclined to change the photos, but, if they aren't what you feature on your site, then they'd have a point.