How do you respond to a 6 year old going on 26?

The 6yr old sister of my hubby mimics how grown ups talk, as in she will says stuff like "Oh how are the kids doing? I cant wait to see the grandkids" Lately she has been asking really personal questions right in front of her parents and they dont say anything to stop her. She will ask stuff like "When are you and so and so gonna get married" or "Are you guys rich?" Not typical kid questions. Personally I think it is rude on the part of the parents because they dont teach her manners but Im not sure how to respond other than "Why do you want to know" How can I get my point across that I dont think this is cute and that she shouldnt be asking questions like that?