Ending

The last scene in the movie I did not realize. Why they killed those two guys?

I do not know, maybe I'm wrong. The first thing that is apparent is that guy in the black T-shirt belonging to a higher social class. This is indicated by the funds they own. I believe a girl and two boys with her, belonging to a lower social class and does not submit rich daddy's sons. One guy wears a black shirt of Charles Manson, but he dont know anything of him. He's just a poser. Is that why they kill him and his friend?