I honestly cannot tell. The sheer size suggests prosthetics, but there isn't the usual "collar/choker" covering up the "seam" at the neck. In some of the pics, the breasts look appropriately squishy (bulging out of tight bras, etc.), which is something I'm not sure the fake ones can do yet. But natural breasts of that size would definitely show at least some sagging....
Oh well - it's all about the fantasy, so it shouldn't matter.
Right?