"You are one ugly mother--"
The Predators didn't arrive until recently, less than 3 weeks in terms of gameplay. There are three groups of Predators, one on each of the main continents. Each of these groups contain about 20 Predators, but only three or four in each of the parties are full "Blooded" Predators, the others are youths and this Alien Hunt is their initiation into adulthood.
The Predators weren't expecting Humans here, the egg pods were placed by remote drone. They also weren't expecting this many aliens, it was supposed to be a "controlled" hunt. The young predators are now thrown into a war against the aliens, and some even want to hunt the prized "ooman" trophies. The game just got that much deadlier with their arrival.
Players are allowed to use the younger Predators in their stories, but not the party leaders. Again, that is the GMs domain. You may hunt, be hunted, fight aliens, fight humans, fight both, survive, or die.