Given how large the hive is, just how many colonists were killed off, because the numbers you face in the Marine and Predator campaigns indicate potential thousands of people died.
The Young Blood's situation. They are out on a hunt, and then all of a sudden, they get swarmed by hundreds of their ancient enemy. You really cannot blame them for calling for help.
The dialogue lines from the Marines indicate that Weyland Yutani's actions have become commonplace. In other words, Wey Yu has the blood of thousands of people on its hands.
Why do the Xenomorphs follow Six? In insect societies, which the Xenomorphs obviously are based off of, women who are designated to lead are given full authority. Therefore, the other Xenomorphs know that Six is their future queen.
When the Rookie is making his way through the Hive he runs into only a handful of xenomorphs, rather strange given how close he is to the Queen and considering how many adult xenomorphs we know are running around the area. However it turns out that Dark, the Predator player character, is also invading the Hive at the same time as Rookie, forcing the Xenomorphs to split their defenses to try and counter both players.
Why do you seem to have so few allies in the colony? Specimen Six has slaughtered the majority of Marines earlier in the day and as a result, the few survivors have largely regrouped.
At first it may seem strange that the Matriarch was killed by fire when fire hasn't been shown to be a very useful weapon against xenomorphs throughout the franchise, usually just causing some pain and maybe making them back off temporarily. However the reason the Matriarch is immune to the Rookies weapons is because her carapace has grown so hard over her millenia of life that the bullets can't penetrate it. The harder something is the less flexible it is, combine that with the fact that when something is heated it expands, and the Rookie caused the Matriarch's body to expand beyond what her aged carapace could compensate for and her flesh basically popped.
