I don't know for sure. It could be a family member, like a mother or a father who has to bear the brunt of the problems in the house.
Maybe there is a young protagonist in the 'house of pain novel'. This character might be the one who observes and experiences all the pain and tries to make sense of it. They could be going through the process of growing up in this difficult environment, facing things like family breakdowns or financial hardships.
There could be multiple main characters. It might include an elderly person in the house who has a lot of wisdom but is also suffering from their own past traumas. And then there could be a child who is innocent at first but is slowly influenced by the pain around them, and their character development could be a major part of the story.