“Skywalker” as non plural feels very palpatine. I hear his voice when I read the title.
He’ll have to wait on international translations to know if it’s singular or plural. That’s being said, I considerer they made a mistake with TLJ translated in plural in french, whereas Rian explained it was meant to be singular.
L’apogée de Skywalker
ou bien
L’apogée des Skywalker