Assuming the system below (solid is waste, dotted is vent).
Do I need vents for the Sink C, Toilet C and Toilet B? They are connected to the primary waste line which is vented at the end of it.
Sink C and Toilet C are in the first floor, all the rest in the second floor.
The distance between the toilet C and the junction with the main vertical waste is less than a 1 meter. Here is a top view from the system: