Amy's full name, Amy Rose, is a reference to the Sonic the Hedgehog character with the same name, Amy Rose.
The film that Steve, Gavin and Amy are was actually the 2013 Carrie film. Though the scene shown from the film is a man in a mask setting fire to a building, the sound and the music is from the Prom scene from the Carrie film. This was an obvious reference to the fact that the first Origins film is based off the Carrie film.
In Herobrine Origins Part III, Gavin's phone ringtone is the Spider-Man theme song, this was a reference to Gavin's actor, David Figueroa who plays Spider-Man in EliteProducitons' Spider-Man: Dawn of Carnage series.
No one is quite sure if Steve is a hero or a villain. Will Evans, the films director has said even he isn't sure what you would call him.
Though never mentioned in any of the films, Jack Briggs does posses the Brine powers, but it isnt as powerful as Steve or Robert's powers.