Compared to Kiku, Yamato is in a gray zone with the pronouns. The beast pirates consistently used he when referring to Yamato, Yamato says Kaido's son, and uses the male bath. However, the vivre card and some other statements use 'she' or female. Since those that knew Yamato the best used 'he' when using pronouns in the manga and anime (Ulti, beast scrubs, etc.), it is really fucking stupid to be upset that some people in the community choose to use he. Oda can provide more clarification with when Yamato interacts with the rest of the SHP as the soon to be newest crew member.