Elsewhere in that same trailer, we see a flying Iron Man suit that Tony jumps into. The back of the suit is open, and he leaps into it, then takes over. This suggests that these suits may be remote controlled, so it's likely that most of them are empty in that image.
It's unlikely that if there are pilots in the suits that they would be Avengers, as Kevin Feige, Marvel Studios President stated in an interview:
Journalist: After cell phones came out horror directors had to come up with elaborate ways to explain why people wouldn’t call someone on a cell phone for help, now that all The Avengers know each other do you have to come up with excuses for why Tony Stark wouldn’t reach out when he needs a hand?
Feige: It’s a good question, and it’s sort of half and half. I am betting that like the comics you don’t have to keep – if you are reading a standalone “Iron Man” comic, they don’t spend every page explaining where every other Marvel hero is. The audience kind of accepts that there are times when they’re on their own and there are times when they are together. I’m betting that movie audiences will feel the same way. That being said, there is a little bit of lip service here and there to that. There is also just the very nature of Tony wants to, once he barely survives that house attack you saw today, and even you saw it in the message he left for Pepper, he’s basically saying “I’m going off the grid to try to figure something out.”
It's currently unknown who is controlling them remotely (Tony, JARVIS, a villain, etc.), as the film is not yet released. It's likely that Tony is doing so, as in a previous trailer (Trailer 1 at 0:27) we see him wearing a device on his head and remotely guiding components of a new Iron Man armor onto himself. In addition, it's been discussed in interviews that the movie will adapt the Extremis storyline. In that storyline, Tony gets some augmentations to himself, which allows him to remotely guide and control Iron Man suits.