I'm getting behind in the discussion again, but I did read about one of the older sons taking college classes, and saw a screenshot of what was reportedly his transcript.
IF that is actually his transcript, then I definitely have a lot of thoughts about this. I was very surprised at the classes he was taking, and the grades he got. Shocked, actually. Those were not junk Underwater Basketweaving classes. One of them is an algebra class. It's not really a "remedial" level class (at least not I guess what I'd consider "remedial".) It would be considered as more of a refresher class if you were a bit weak in math, or would be for someone who is maybe going back to school and needed a refresher course. It would be only one step down from an algebra class that you would take towards one of the core classes you need to get an AA degree.
This kid was taking classes that many other normal college students would have been taking. At least the math one.
This leads me to believe that the kids are NOT as "feral" as some people are thinking. At least not the older ones. Yes, I'm sure they do have cognitive problems because of many years of malnourishment, isolation, and just the emotional trauma of being horribly abused for so long. But they apparently have some knowledge of the outside world. The son that took the college classes had skills in at least high school and even lower level college algebra, especially considering his grades! I don't know how the hell he did that considering his nightmarish home life, but somehow he did. He also would have seen how different the other students were. He would have seen them talking, laughing, and socializing normally. He would have seen that they didn't have the same feeling of fear in their eyes and body language that he had. He would have known, ABSOLUTELY known, that other people did NOT live the way he and his siblings did.
This leads me to thinking of yet another reason why the kids were so afraid to try to escape before. They were brainwashed, yes, but I think considering how horrific the abuse and torture was, I think there must have been something else that stopped them. I remember reading an article that mentioned how neighbors in Texas sometimes saw the "dad" outside target shooting with a handgun. Maybe you see where I'm going with this. That psychopathic creep was ARMED.
My theory is: The kids knew how sadistic and ruthless their parents were. They knew their evil creep of a father had a gun, and were afraid of how far he would go. Even if one or a couple of the kids were lucky enough to be taken out of the house occasionally, maybe they didn't try to make a run for it because they knew their other brothers and sisters were at home with the monster...who had a gun.
This is all just my speculation. But I'm thinking that if the monsters thought that starving the kids wasn't enough to weaken them into submission...well, "dad" could always take out the gun for a little extra reminder. Or maybe he didn't even have to. Just the knowledge of him having it could have terrified the kids enough.