My guess for this is that there will be eight posters total. From Black Widows poster we can see she is flanked by Hulk and Thor, the blue streak in the back is surely Quicksilver who will likely be positioned above Iron Man. From Scarlet Witch we can see the arrows telling us that she is next to Hawkeye. With the huge ensemble cast of this film it would be possible that we’d get more: maybe Fury, Maria Hill, or even Vision or Ultron himself. But I’m inclined to doubt they’d fit in with the action scene depicted. Besides at the rate of two posters released a day, they’ll be at 8 posters just in time for the Marvel panel at SDCC.