The Great Gatsby, stage-twins

I'd like to know if "a pair of stage twins" in the chapter 2 of The Great Gatsby refers to "twin stage actresses", "stage actresses who are twins", or to girls who play the parts of twins in plays?

A pair of stage “twins’— who turned out to be the girls in yellow—did a baby act in costume and champagne was served in glasses bigger than finger bowls.

Thank you.