I don't think I could reasonably dictate what anyone else wears.
And let's face it: plenty of people go to the beach just to flaunt it. So, it's pretty much anything goes (insofar as clothing is concerned) at the beach anyhow; outside of complete nudity, of course.
Maybe a better question is: how do you feel about it?
If any particular aspect of your physique is on display, essentially: would it bother you if, potentially, anyone looks? Including his parents.
If so, I would adjust accordingly.
I'll be honest with you: there's nothing more appealing than a woman's body. Adding confidence to that would only make her more so.
In fact, sometimes: her confidence alone--genuine confidence that is--is enough to be sexy.
Still, I at least (and most dudes, I hope) would know better than to be annoying about it.
Don't tolerate anyone's shit, of course. But ultimately: do what would make you feel comfortable--with the understanding that: that is also, naturally, a product of the group's overall comfort.