I've had my own observations on this through the years:
A family unit is like a mobile over a crib - each component has a "role" as the unit seeks equilibrium. This is a reality in every family and is not restricted to the "dysfunctional" ones. It is how a unit, comprised of different people, survives; and this is not to be seen as evidence of a dysfunctional system. This can be seen in any unit - at work, at church, in any organization.
But here's the difference. The more dysfunctional the family, the less ability for the different members in the family to be fluid in what role their personality bends them to. In other words, in the alcoholic family, the child who is the "scapegoat" is always the scapegoat. But in a more healthy family, that child may be a scapegoat in some situations but in other situations be any other role and in his/her whole lifetime have been in all the roles (except those restricted to the parents). The roles always have to be there for the unit to exist, survive, and thrive. But individuals within the unit can change roles without the unit becoming so out of balance that its existence is threatened.
Just my thoughts. Hope that helps somebody, anybody.