Families are a knot of strings. Some tie people together and some hold people apart.
The best way to visualize this is to imagine a house with a fence around it.
The typical white picket fence is the normal, healthy boundary that lies between the family members. This fence shows a clear deviation between the yard and the road, but still allows for visitors to come and feel welcome.
The wall of stone around the yard is an example of a ridged boundary, one where no one is allowed in or out. Hidden behind this wall, a member of the family separates himself from the rest of the family and will not let anyone into their mind or train of thought. These members of the family are very exclusive and can be very protective of him/herself as well as those in the family.
The lack of a wall around the yard shows the lack of any boundary. In this, there is no structure to the family and the members though do have a bonding, have no means of stability.