Two observation-opinions:
1 Lori-Chad minimized other people and labeled them non-people, and thus expendable, making it only a matter of time until the kids would inevitably end up deadified for being in the way. But I do wonder, rather than a deliberate, planned, scripted act, were one or both of the kids killed by "heat of passion" events, particularly by Lori?
Why? Because the more we see and hear of Lori, we learn she was extremely volatile (befitting her self-glorifying approach to life). She was Little Miss Sweetness until you crossed her, and then the exact opposite. Cruel. Hard. Angry. Willing to crush. So I give her credit for the ability to be so angered that she could kill, and then clean it up later with self-delusion, lies, and whatever it took to make her feel justified.
I'm not saying that was the plan. But rather, I really think she could have gone off script, so to speak, because in the spur of the moment, she just didn't want to put up with x y or z.
2 We see a lot of talk about people who supposedly had evil spirits. Then we see these violent, volatile, utterly self-absorbed, evil people doing whatever catered to their own desires, and I truly (yes truly) wonder -- are Chad and Lori the ones who actually do have evil spirits living within them? The casual evil full-ego actions and the way they manipulate others sure seem like that's possible. Just saying.