Don't worry there deffinatly will be some 'safe house love' scenes lol :P there's also the fact that at first no one knows it's xenomorphs, and that none of the marines know what they are with W/Y having covered up all the evidence of them. At this point everyone thinks it's at best a downed transmitter, and at worst just some terrorists or rebels with really crappy weapons/what ever they could grab to defend themselvs.