Without being able to examine them in person, it's impossible to determine their authenticity. However, just based on the pictures (which are of poor quality), if they are fakes, they are very well done. The cranial sutures, the septum, the tendency for holes to form in the orbital bones when the bones get excessively dry and brittle from not being stored correctly, the set of the teeth in the maxilla, the overall contours and proportions, are all accurate for a real human skull.
What's going on with the mandible is interesting. It was either a very poorly preserved mandible that has suffered extensive damage, or the mandible represents someone that had all of their lower teeth removed likely a number of years before their death. The remodeling present would be indicative of someone who wore dentures. This would mean that the skull belonged to someone who died at an advanced age, and if so, more likely than not from natural causes. Based on the lack of frontal bossing, and the mandibular angle, I would say the skull pictured with the mandible is that of a human female.
That's about all I can get without better pictures.