Welcome! I am glad that you made it away from your husband. You're very lucky! I bet it was very hard to get away from.
From Wikepedia, NPD can be defined as:
A pervasive pattern of grandiosity (in fantasy or behavior), need for admiration, and lack of empathy, beginning by early adulthood and present in a variety of contexts, as indicated by five (or more) of the following:[1]
1) has a grandiose sense of self-importance
2) is preoccupied with fantasies of unlimited success, power, brilliance, beauty, or ideal love
3) believes that he or she is "special" and unique
4) requires excessive admiration
5) has a sense of entitlement
6) is interpersonally exploitative
7) lacks empathy
8) is often envious of others or believes others are envious of him or her
9) shows arrogant, haughty behaviors or attitudes
From my own personal knowledge of Brad, I would have to say that he would easily fit into 1, 2, 4, 5, 6, 7, 8 and 9 (unless he has managed to outgrow previous behaviours, which I don't think would happen without a lot of therapy). I believe that in not wanting the kids to go to Canada was just yet another form of control.
Brad controlled Nancy financially by giving her an allowance, not allowing her to earn money on her own, removing her from bank accounts and household accounts, not to mention taking the kids' passports. I also wonder if he drug his feet on helping her to get a work visa so that she might have the ability to work (which would also give her a better ability to leave him).
Unfortunately, I think he had a lot of control over her because without his ok, she could never leave the USA with the kids. She was a great mother and she was never going to leave her children with him in order for her to get away from him. And now, sadly, she has paid an awful price.