Nothing happened to the elder since the ship that blew up on earth was a scout ship. Not sure if you guys saw the part, but the mothership leaves earths orbit just after taking scar on board, they hit ruffly around saturn in the mother ship when a scout ship departs from one of the bays and heads back to earth. The ship was problably equipped with 5-9 preds maybe.
I would say why the preds were armed, they are a race of warriors, living for the hunt. They would be bad hunters if they had there pants down at the ankles if someone came on board and killed them. I say they prepare for anything at all times, I could see the one who was leading the "party" with the eggs he was checking the area as they went through the ship. Most likely they always stay on high alert at all times. Just my thoughts.
I also had a thought on why the predator shot at the hybrid in the ship, I think he was a unexperienced hunter. When seeing the Hybrid in his view sight "lights as yellow skin" he prob freaked out and just shot like any untrained soldier. Heck Wolf took all his gear off and charge right at the predalien, and he was elder and experienced so thats what I think the pred shot on the ship rather going after him with his blades. I just cant get over why so many preds died. You would think on all there ships they have some sort of sensor that would indicate aliens on board, and all breads of aliens since they have hunted them for years. I mean they carry eggs on board.