I get the feeling that Marc's sister (who owns and lives in this Château with her family and kids) didn't have the faintest idea that Stephanie and her cameraman would film every corner of her home and make a 47 minutes vlog of it for her YT channel.
Just look at Marc's face when not interviewed.
This Château is lived in by REAL people with a real life.
It's not because you're from an old aristocracy family (their case) that you have money. Plenty of aristocrats with no money in France and have to work like the rest of the commoners (unlike UK I believe ?). Marc is a agronomy engineer or something like that.
Their champagne business is just that : a business. And cash is not necessary in your pockets.
Plus, they don't try to show off, to prove the entire world that they are what they're not IRL (like someone we know).
I'm pretty sure that the sister is not really happy (maybe even mortified) to know that her family home has been filmed that way by total strangers.
What were Amy and Marc thinking in doing this ?
Did they want to know what the priestess was like in real life ?
Did they want a boost for their YT channel ?
IMO sister and brother relationship got a hiccup after that