I think if the rich family knew what the hidden family was doing they would have fired her and called the police. I think that's a totally normal and understandable reaction, but it's not the most moral reaction, which would be to help the hidden family. I think this cuts against your argument because the richest people aren't extremely moral, whereas they would be if point was that morality follows wealth. Consider the party scene where the rich father cares more for his fainted son than the stabbed poor daughter.

I think your attempt to perceive and expose my biases is unsound. I called her a diligent servant because she is, and to contrast her with the poor family. The diligent servant works hard, does her job, and earns even the extra she takes for her husband. The poor family don't really know how to do their jobs, consider the father's inattention while driving or the daughter's made up therapy, and they perform their jobs haphazardly.

The diligent servant is doing what she's doing because otherwise loan sharks will kill her husband. The poor family is doing what they're doing to make more money. The point is that the original housekeeper is behaving morally and picking the best of bad options. The poor family is behaving immorally by lying, getting people fired, poisoning the housekeeper, and stealing. Both are poor and only the main family is immoral, which again rebuts your interpretation.