Wrt NCSU, it may be that many kids from your school chose not to attend so they figured, why bother, lower our yield rate for rankings, and complicate things for yield management when we can save everyone the bother? (You can try and see if you can have College Advising at your school calculate how many students who applied chose to attend - if it’s below 20%? 10%? you have your answer).
I agree your son has the stats for NCSU engineering (I’m assuming he took Calc and Physics, got As) but since it was far from his first choice, 
… and he’s got 3 good choices.
Since he doesn’t want Greek, Wake will be limiting socially. It’ll also be the most familiar, can be a good or bad thing. Less specialized, also a good or bad thing, strong sense of community. Not especially known for Engineering but excellent general reputation.
Penn State will always be hard to get to, which will mostly matter at Thanksgiving and Christmas - I assume he’ll fly; if driving, consider winter weather. If he didn’t get into or didn’t apply to Schreyer, he can apply to the Engineering living-learning community (it has a secondary application linked to the COE) or the more general LLC for science&engineering students. LLCs create a sense of community and are housed in better dorms (West) than the party dorms (East). Engineering classes will be large, and tough. Since he has AP credit, he could take fewer credits his 1st semester to adjust.
Northeastern: how compatible with engineering are the London/Oakland programs? How enthusiastic is he about moving from place to place? Some students love it, thrive and are energized by the change - and thus love the co-ops, which follow the same “off campus” model. Others can be unsettled by switching places all the time and having friends scattered all over. Finally, NEU is very preprofessional, its point is the organization of co-ops, in a sense opposite to Wake. Does he have a preference between the 2?