Fourth one is a U.S. antiaircraft gun (obviously). With a couple of GI’s
Although carrying a “US” star, by 1944 most allied armies used the “US” symbol for recognition purposes (edit - BT White in "British Tank markings & Names, A &AP, 1978, ISBN 0-85368-222-4, dates this practice from mid 43 in preparation for D Day) , so a white 5-pointed star with or without a circle does not always mean the equipment is from the US Army / AF.
Edit - the Free French used both the “US” star and Free French symbol (a stylised white outline map of France in a blue circle, with Cross of Lorraine) at the same time on the same vehicle (plate D, Vanguard pub 31 - US Half Tracks of WW2, S J Zaloga, Osprey, 1983) and the Brazillians used their own white cirle containing 5 small white stars (plate C, ibid).
The equipment shown is actually British, a Mounting, Triple, 20mm Mk1, probably in British service but may be from another Commonwealth army (note the British pattern helmets thus very unlikely to be US or Free French).
The guns are either 20mm Oerlikon or 20mm Polsten. I think they are Oerlikon as the barrels seem to be stepped into three parts, as opposed to the Polsten which has a much less pronounced second step.
However, as the Polsten was pretty much a simplified version of the Oerlikon (modified initially in Poland, then made by the STEN company in the UK) they are very difficult to tell apart. The usual recognition point of the magazine shape (rectangular for Polsten, round for Oerlikon) cannot be seen in this photo, which leads me to think it may be a staged photo.
I shall cogitate on the other pictures and see if there is more information I can give. I’ve seen pic 1 before, but I can’t remember in which book.