Hickey was looking forward for the last two shots and definitely recalled the last shot striking JFK in the head. He said that the second shot did not appear to hit JFK. It appeared to miss. All he saw was the hair on the right of JFK's head fly up at the time the second shot sounded. Guess where that occurs?
Brehm does not necessarily describe the headshot as the second shot. He said that JFK's hair flew up on the second shot. That is what Hickey saw as well on the second shot. Brehm was never questioned by the WC. It is difficult to determine what he saw. Hudson gave two statements shortly after the events (November 22 and 25, 1963) and gave a very different statement in his testimony in July 1964. If you go by his first two statements as being the more accurate, he says that JFK slumped on the first shot and the last two shots were in rapid succession. He does not say which of the shots hit the President in the head. He does not even mention a shot hitting the President in the head.
It was not a matter of not hearing a shot after the head shot. It is a matter of hearing and/or seeing the head shot as the third of the three shots. The Connallys, Greer, Hickey, Powers, Bennett, and McIntyre all recalled the head shot as the third shot. Hill recalled it as the last of two shots that he recalled but believes, based on what other agents said, that there was a second shot while he was running beside the left front of the QM.
The statement I use for Brehm was given on 24th November, which I read as meaning the second shot was the head shot with short gaps between the shots of a few seconds or more:
When the President's automobile was very close to him and he could see the President's face very well, the President was seated, but was leaning forward when he stiffened perceptibly at the same instant what appeared to be a rifle shot sounded. According to BREHM, the President seemed do to stiffen and come to a pause when another shot sounded and the President appeared to be badly hit in the head. BREHM said when the President was hit by the second shot, he could notice the President's hair fly up, and then roll over to his side, as Mrs. KENNEDY was apparently pulling him in that direction.
BREHM said that a third shot followed and that all three shots were relatively close together. BREHM stated that he was in military service and he has had experience with bolt-action rifles, and he expressed the opinion that the three shots were fired just about as quickly as an individual can maneuver a bolt-action rifle, take aim, and fire three shots.22H837
https://www.history-matters.com/archive/jfk/wc/wcvols/wh22/html/WH_Vol22_0434a.htmHe explained this shot sequence very clearly in 1986 with the aid of a map:
As for Emmett Hudson, his early statements are lacking in detail, but by explaining more in 1964 I would say that we can use that as his clearest view of the events. I don't think anything he said later contradicts the early statements, he merely gives more information.
Yes I agree with you, several witnesses do regard the head shot as the third, which contrasts with the others who said the head shot was the second shot. Although superficially the Dealey Plaza witnesses seem to contradict each other on this point, I think it is possible to make sense of their testimony in terms of each of them only hearing a part of the gunshot sequence. Some witnesses missed the first shot, some missed the last, and others heard double bangs instead of a single shot (especially near the head shot). Overall they cluster around three clear bursts of gunfire relative to the Zapruder film:
This pattern also matches those who reported three separate shots, and also those who said the last two shots were closer than the first two. It seems to be a rather neat way to explain the otherwise incongruous witness statements. The only remaining issue to untangle is whether a single shot was fired in each burst, or whether a pair of shots was ever fired (i.e. two gunmen versus echoes from a single shot).