The father and mother repeatedly remarry each other and have children from previous marriages. The children raised in this environment are brothers and sisters, but they are not related by blood. They literally live a makeshift communal life as a family. As the parents' sense of ethics has collapsed, the children are similarly detached from the world. This situation could be called abnormal, as their sexual desires are directed at the closest family members. However, for this family, it is normal. Mother and son, father and daughter, brother and sister... and orgies. It's hard to understand, but this is common sense in this household.