You guys need to pay more attention to the books O_o
James got a needle in his thruster, making him spiral off to space.
In the trailer, that is probably him (I think it looks like a Station, not a Frigate).
The "second" body is just a piece of flying debris.
Fred died when he detonated a nuke on Onyx. He did it so none of the Covenant would get to the rest of his team.
On the station with James was John (Master Chief) and Linda. Linda was on the Pillar of Autumn with Master Chief in Halo: CE but was too injured to be put out of stasis.
James, as mentioned earlier, was thrusted into space.
Fred and the rest of the Spartans were on the ground on Reach while James, Linda and John were on the orbital station.
If you want to know about Halo but not read the books, have a look at Halopedia.