This is a difficult one. Black Zetsu is not technically a human, and whether or not he is an actual living being is disputed, even though he was in Akatsuki as part of Zetsu. Madara thinks Black Zetsu is the manifestation of his will, but in reality, Black Zetsu is the living expression of Kaguya’s will, created by her before she was sealed as a conduit to her can return. Black Zetsu essentially manipulated the Uchiha to the point where Madara thought the Infinity Tsukuyomi was what he found out about, only when Black Zetsu betrayed him and revealed that Kaguya was pulling the strings.
Thus Black Zetsu was either Kaguya’s creation or Kaguya herself, or potentially both. As her creation, he is like a brother to Hagoromo, which is more directly related to Naruto. However, as Kaguya, he is still related to Naruto, just one more generation back. So he could be Naruto’s super distant uncle or his great-grandmother.
https://www.looper.com/765517/the-naruto-family-tree-explained/ Naruto Family Tree Explanation