I don't doubt at all that the abuse took place. I believe they were abused from a young age and that they were deeply, irrecoverably damaged as a result.
The problem comes when they basically planned out a cold blooded brutal murder days, weeks and possibly a year in advance.
The question I had was why didn't they just leave. I get that people will say its very hard to leave a domestic abuse scenario and that they shouldn't be blamed, but they could both have literally packed a bag, walked out the door and started a new life anywhere. They didn't have kids, they hated their mother and they were confident enough to go off to college and have social lives. Lyle was at Princeton and Erik modelling.
I think they were so used to the lifestyle they lived they didnt want to give it up. They possibly thought they were owed the money for what they suffered and thought taking their parents out of the picture was a better solution. Which is murder, no matter what the situation.
If its true that they were considering killing the therapist as well shows how dangerous they actually were in their determination to cover up the crime. They were very calculating in how they planned it and tried to get away with it, it wasn't an act of self defence.
I think life in prison was the right decision rather than the death penalty. They were a product of their environment. Whether they should be released now is an interesting question.