1. Always possible, but if AG was in the plan, I'd view her as the victim. She did stand out during the family interview but mostly because she was trying to suppress tics. (IMO. All three children looked rather introverted to me, btw. Was it mom's trait? Was NG not too extroverted, probably not an idle talker, a smartie, an independent woman who made it even when got she widowed, until this happened?)
So if AG's husband was involved, he probably did it behind her back, or intensely manipulated her.
2. Highly possible especially if NG partook in SG's show. All one has to see is that the daughter is successful and mostly, loving.
3. Also highly possible. I'd bet on the abduction being for money in this case, and the person being "upset" with NG for being "too critical" or such. I know such a story, with a much younger victim. The person had a prior (concealed) criminal history. I'd add people from the "hired helper's" family to the group.
4 or 5 - sounds unlikely to me. If it turns to be 4 or 5, then, sadly, the world is even crazier than we think. I know things happen, but it is still unlikely. Although an "incel-type" could organize things easier from the standpoint of ransom notes, or such.