The nature and tendencies of family dynamics fall under the archetype of Cancer. Cancer, as an archetype, is a sign that is strongly focused on the past, stability, and comfort.
Parents, whether they are conscious of it or not, can raise their children based on their own life experiences which is essentially their past. The reason why there are strong familial trends in the natal charts of families is because there is a constant passing of past trends from one generation to another. The trend is strong because there is a strong connection to the past, which is ruled by Cancer.
Change is also something that can be seen as a threat for families, which is ultimately a threat to Cancer as an archetype. Cancer strives for comfort and stability, and any change of any sort can shake up a family dynamic. For example, having a parent suddenly losing a job, a kid graduating from high school, the mother having a new baby… These are all events where all members of the family must go out of their comfort zone and perhaps painfully, but effectively adjust to new situations. Going through change in a family can often feel very volatile, as if a structure of some sort will collapse.
This is why families can be private from the outside world. Family can be even be seen as an escape from the world or even be against it. Families, like the Cancer archetype, have a very strong, protective shell to protect itself from change, which is stimulated by the world. However, the Cancer archetype as a cardinal sign will only work well through change, and individual families may struggle to realize that change, although uncomfortable, could be the only thing that can save its existence. The changes in the world around them constantly challenge the strong values, foundation, and base established in the family. These challenges can either destroy or make a family stronger.
The actual workings of a family can truly be a mystery for anyone. Like the Moon, the ruling planet of Cancer, the family is always constantly changing within itself. The idea of family is often fluctuating and fluid, just like emotions. In a way, this can help a family adjust to any sudden changes brought onto them, but it can also bring a struggle of stability. This is why families can be quite shaken up when a change comes onto them because there is already a sense of change and fluctuation within the family itself. There is already a simultaneous sense of stability and instability and having a polarizing, hard to understand characteristic while having a major change can be quite terrifying.