The main poster for "Red 2", with the cast walking towards the camera from out of the shadows, may have been indirectly inspired by the poster for The Wild Bunch (1969); that poster shows the cast (including Ernest Borgnine) walking out of the shadows away from the camera.
Why did Marvin fire the AK at the helicopter towards the end?
Marvin fires the AK at general area of the helicopter (notice that he doesn't really aim down the sights, he isn't trying to shoot it down or damage it) so it would retreat and get outside the explosion radius. He's making them run away so they survive the incoming explosion.
Who will be the new actors in this movie?
Anthony Hopkins will play a character called Edward Bradley, a believed dead scientist who created a nuclear weapon. Catherine Zeta-Jones plays a character named Miranda Wood. She is a high-ranked Russian spy and former love interest of Frank. David Thewlis plays "The Frog," a character selling major intelligence for a price. Neal McDonough plays Jack Horton, a character from the Pentagon after the nuclear weapon and Frank Moses. He is the secondary antagonist. Byung-hun Lee plays Han Cho Bai, the best assassin in the world, contracted by Jack Horton to kill Frank Moses. He has a personal conflict with Frank, because Frank betrayed him.