This PAK came with the kfz 70 truck which was used to tow it. The PAK 36 was a 3.7 cm caliber weapon. It was the main anti-tank gun in the German Army until mid 1941, when given its inability to deal with the soviet medium tanks liek the T34, it was replaced by the PAK 38 which fired a 5cm shell. The PAK 36 was initially issued in 1928 and first saw combat in 1936 during the Spanish civil war. It was also used by the Chinese against the Japanese where it was a lot more effective neutralizing the lightly armored Chi-Ha tanks.
Not sure it these guys were meant to be US troops or Italians, but since I already classified the guys in the previous picture as GIs I'll do the same with these. I found them as part of a larger batch of Atlantic figures. It is hard to tell what exact set(s) they were released with. From what I have seen, some of these figures were released as part of multiple sets. For instance, the guys with the radio were released with the rocket launcher, but also with an artillery set. The other two guys are more easily associated with an artillery crew. And I even got a small ammo stack to go with them.