This is kind of like when a really budget television show can't be bothered to hire actresses who look anything alike to play siblings and rely on the strategy of "similar outfits" as a shorthand for "shared genetic material".
Although why the US chain store Target would be hiring Hailee Steinfeld, Jessica Chastain and Brooklyn Decker to play sisters at their The Shops At Target party is a mystery to us.
In fact, it seems completely unlikely so we've come up with a rival theory: That the stylist who works with The Saturdays was helping the ladies pick their party attire but there was a massive falling out over whether Jessica Chastain would have wavy hair (she refused) and the stylist left the girls to pick their own shoes and see how they liked THAT.