I am not at all surprised Kylr put them in the same place - other than it feeling safe, I think it is part of his mental makeup to put his victims together. It makes it easier to revisit. He would not have stopped at Jessica.
Jessica would be pretty skeletal by now, 6 months later, especially if left nude to the elements where animals and other scavengers take over. This is also likely why all the bones have not been recovered - if they were buried, it may be a few days before they are fully excavated. Just mentioning the skulls in headlines is more shocking and alludes to there being a possibility of identification. I believe they have a solid idea this is the girls due to notifying the parents and the information they are releasing to the media, but obviously need an ME confirmation before it is official.