I suspect that these "extra smells" are subjective, and that there's no chemical basis for any of them. When it talks about how brothers and sisters can't sit

I suspect that these "extra smells" are subjective, and that there's no chemical basis for any of them. When it talks about how brothers and sisters can't sit too close together because "their smells would mingle", they could have easily substituted in the words "auras" or "mojo", and it would have the same semantic meaning. It's more interesting to speculate on why they would develop these subjective values in the first place, than it is to wonder why they've confused those values with actual odors.