Это в его духе. / Это в её духе. / Это в их духе.
I assume this is a figurative expression with the meaning of "it sounds like him/her/them".
(в = followed by the prepositional case)
(его/её/их = genitive case)
(духе = prepositional singular case)
My question is:
"их" is plural, so shouldn't you say "Это в их духах" with the prepositional plural case instead?
Why is it incorrect to say "Это в тебя духе" оr "Это в вас духе" to mean "that sounds like you"? Even though they share the same construction?