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:
Best Answer
I'm answering my own question since I changed the design based those comments here and on some other research (code and recommendation).
Sink C now has it's own pathway to the "junction box". The vent on Sink C joins the main vent stack above all and acts as a wet vent to the junction box too.
Toilet B doesn't need a vent due to distance to the main stack.
Toilet C is of a little concern because it is "wet vented" by the main stack, but since the piping there is 4 in I doubt that it could create enough back pressure to break the Toilet C trap.