how to activate the guns and turret simple change different camera the 20mm will automatically activate the 20mm group and along with the turret(no group needed on the turret)
Turret can be control in camera each.
20mm will only group activation on camera each that's it.

To know the about the PB-1 here's the post site with the lore of it: https://www.simpleplanes.com/a/8exU61/PB-1-Medium-bomber

(Disclaimer this is a fictional lore not a real life base story)
Lore: During the battle of Mindanao in February, 10, 1941.
PB-1 Medium Bombers are slowly getting destroyed and unable to bomb more targets against imperial japan Philippines air force started to fund another bomber but it's much more cheaper consider how low the Philippines military budget they have.
so the engineers decided to use the
PB-1 frame body by extending it longer and more bomb bay for increasing the capacity from 8 to 16 100kg bombs,
Adding two more engines totalling it by 4 engines, and naming it the "PB-2 heavy Bomber" and the gunners stay the same and the maneuverbility of the PB-1 is still their which is surprising despite its heavy but somehow it's maneuvable, but they sacrifice the front machine gun
for maneuver escape the bomber out of the danger zone and only 30 were built in the Philippines Air Force and after they entered service in October, 6, 1941
The heavy bombers were successfully bomb bigger and multiple targets through many missions and Imperial japan are struggling to counter attack again against the heavy bomber for how maneuver the heavy bomber is and Imperial Japan soon will have their own fighter plane to counter it.