Random question about your INTJ son: How old is he? Supposedly, outside of an F type, INTJs are the type most likely to be emotional due to their tertiary Fi. I think that, if the goal of an INTJs life is to understand people, he can be just as apt at it as an INFJ but in a different way (Ni would give him various insights into what might be happening and Fi would help him sympathize with people and understand what is going on and how various people would feel in that particular situation.) There's actually quite a few INTJ writers who are very insightful into the nature of human nature because of the shared "Ni" INTJs and INFJs have but also the shared Fi of INFPs and INTJs. Their characters tend to be more...solid. I suppose. It's hard to explain. That might be a good topic though, the difference between the writing styles of Fi and Fe.