Chosen child

How might one account for an adult who fails to leave home, fails to develop a strong will, forms a smothering bond with one’s mother and lives with and cares for her until her death?  This child is chosen from among his / her siblings.  At an early age the parents commence their corrosive gradual erosion of this child’s self esteem so that during the age of individuation, adolescence, this child remains psychically attached, always seeking approval that is always withheld.  This is a conscious or unconscious strategy to ensure a caregiver in old age for the parent(s).  Husband and wife collude on this culling strategy and enable one another in their project to dissolve the integration of the personality of the chosen child.  This child has been known to murder its parents in order to gain psychic  freedom.