As I understood it's only the scent they have. And yes others know about the scent thing in their family. That's why they were hiding the eldest as she doesn't have a scent and she could tarnish the family reputation.
But in my opinion I think the father still loves her and couldn't be with her as hes gone. I thinks it's like some king of Cinderella story but without the father dying he's still alive. I think the Duke is surprised that she smells nice without even wearing any perfume or something. I think he also doesn't know what she normally doesn't have any scent. Also he's surprised that he's the only one smelling her scent.
Hope this helps a bit
I actually decided to read some MTL of the novel, and the scent thing is a secret that no one outside the family (and I guess the family's servants?) knows about, so they were kinda hiding her for no reason aside from the fact that they suspect she's an illegitimate child lol. They'll reveal it in the next chapter.
What the there is really no point of hiding her when other don't know about the scent thing wow thanks for clarifying!!!!
That is kind of ridiculous, how could you possibly hode such a thing as a smell ??
I wish they explained better what the scent thing is. Does it do anything besides make you smell like flowers? Do other people know about it? If they do, why is the ML so surprised she smells nice when she told him she was from the Fleur family? (since it was apparently a family secret that she doesn't have a scent)