I have only just watched this and haven't looked into the real story.
But I did think there wasn't enough explanation about how the new family and the old family happened.
I sort of assumed that the mother probably had already experienced domestic violence, and sort of accepted this as the price of a pretend happy family. She was obviously medicated and the step dad did a lot of the day to day caring. And hadn't at least one other child been taken into care.
It made me think of those women who time after time have a child, it is taken in to care, so they have another one also taken into care.
Many of us are fed the idea that the ideal is a family, but dont necessarily have the opportunity or maturity to achieve it. So make do with something that approximates it.
This is partly influenced but what the mother said (which I had to play back 4 times and then put the subtitles on) that on some level she didn't care about the step dad being killed or that her sons had done it to proect her because it meant they were no longer all together ie approximating a family.
Everyone seems to assume we will or are natural parents. And everyone assumes we will somehow set up a family.
Nobody every talks about the fact that some of us maybe just aren't suited to do it.
And for too many women still, this is still fed to us as being are top goal in life.