Those are helpful examples, thanks.
The McStay's are a very good example to compare with this kidnapping.
BTW, we don't know everything yet about that case, but clearly info about the condition of the home was concealed by police until after the arrest. Also, the video footage of a family crossing the border was massively misleading. I believe police will keep their suspicions to themselves and allow the public to scamper off on wild goose chases.
Anyhow, as an example of an apparently similar crime, the accused was targetting the McStay's very personally (it seems to me he must really have hated Joseph), he wanted to create the disappearance scenario to avoid detection, because if they'd been found murdered he'd be a prime suspect. He had a plan, and chose his moment deliberately when they were all home. One issue is that, since he arrived during daylight, he may have been welcomed in. He possibly grabbed a boy and could force compliance. Less easy to carry out if he'd arrived 3 am, and with older girls, but as you say, possible.
This now reminds me of another case I'm following, the McFalls in Arizona. The older couple disappeared from their home, leaving everything behind. The suspicion is falling on someone they'd had bad relations with, and who was charged with a crime against them. Having a criminal record would be a big problem for this person. I think that by disappearing them, this person believes nothing can ever be proven, and he is safe.
ETA: so in both cases, the McStays and McFalls, it suggests the motive of someone carrying out this type of crime is a combination of hatred, removing an obstacle in the perp's way, and a strong determination to never get caught.