They aren't a crew of mercenaries either and don't know each other. They are assembled from all over the world after being watched and assessed by the Predators. So Brody is a cop/fed who the predators watched skillfully hunt down and kill a suspect, Trejo is an assassin for the Mexican Cartel, a Yakuza assassin/ninja from Japan, a Russian soldier with a minigun, a hunter from an African tribe and so on. These are all kidnapped by the predators and taken back to their homeworld were they are dumped in the jungle and then hunted for sport by the Predators. They're also hunted by the wildlife/monsters from the homeworld.
It's not written as a shitty "PG-13" action film, it's very violent and gory and best of all there might be a surprise cameo from someone from the first film!
[spoiler/]
Now that sounds infinitely better than a re-tread of the the original
Looks like Brody is beefing it for it...