No, as I said, they would be venially immodest at the grocery store or elsewhere. They would only be worn during volleyball games and practices. Wearing them to Mass would exacerbate the sin, although I would not consider this mortally sinful even at Mass.
Why it's wrong for the coach and not the girls illustrates my point exactly. Coach has no proportionate reason for wearing the outfit (she's not playing), while the girls have the proportionate reason of being able to function properly during a volleyball game and not risk injury. I've attempted to explain the notion of proportionate reason. Coach has none, but the girls do.