I wouldn't call it the plural of your, since it is the same thing as your. But yes you're right.
- you (singular) = je/jij (if subject) je/jou (if object) - Jij bent lief (You are nice) - Ik vind jou leuk (I like you).
- you (plural) = jullie
- your (singular) = jouw
- your (plural) = jullie
Jou is not a possessive pronoun, jouw and jullie are. Jou is a personal pronoun when used as an object: https://www.englishclub.com/grammar/pronouns-personal.htm and https://www.duolingo.com/comment/3852773