The 2 girls at once thing...
I admit to always being afraid of kidnapping/abduction and stranger danger from a young age myself and I have spent many, many hours over the years playing "what if" with my kids as they were growing up. "What if he has free kittens??" "What if it's a lady?" "What if it's just another kid?" "What if they say your mom said to pick you up?" etc - we call this the "what if" game and they also add scenarios and so on. Point being I would assume they are well versed in trickery and are ahead of the curve on what to do if something horrible happens.
I asked my daughters (independently of each other) last night "what if someone grabbed your sister with a knife to her throat??"
To my dismay they insisted they would never run and leave the other behind. I was very encouraging that they could be the only way to get help or they would be a witness if something terrible happened and so on and nope, they 100% insisted they would stay and fight and would never leave even after I insisted that that running is what they MUST do. The fact that they both said this without input from the other is very telling IMO. It must be highly instinctual to not leave someone behind and nearly impossible to convince them otherwise.
Anecdotal of course but this makes me think it wasn't that difficult for him to get both of them to comply. Really sad and really scary.