I think there can only be 3 WHM at a time due to a specific ritual they need to do + the need to limit WHM by the Elementals. Although all Padjals seem to go through CNJ training in Stillgade fane, but only a select few can be a WHM.

The only group of people I can think of that need to have 2 classes as part of the training regimen would have to be the Sultansworn. As far as I know Squires there need to know basic CNJ