The phenomenon of the increased risk of violence and death of stepchildren is referred to as the Cinderella effect. Borderline personality disorder
C-PTSD may share some symptoms with both PTSD and borderline personality disorder (BPD). However, there is enough evidence to also differentiate C-PTSD from borderline personality disorder. It may help to understand the intersection of attachment theory with C-PTSD and BPD if one reads the following opinion of Bessel A. van der Kolk together with an understanding drawn from a description of BPD:

Uncontrollable disruptions or distortions of attachment bonds precede the development of post-traumatic stress syndromes. People seek increased attachment in the face of danger. Adults, as well as children, may develop strong emotional ties with people who intermittently harass, beat, and, threaten them. The persistence of these attachment bonds leads to confusion of pain and love. Trauma can be repeated on behavioural, emotional, physiologic, and neuroendocrinologic levels. Repetition on these different levels causes a large variety of individual and social suffering. However, C-PTSD and BPD have been found by some researchers to be distinctive disorders with different features. Those with C-PTSD do not fear abandonment or have unstable patterns of relations; rather, they withdraw. There are distinct and notably large differences between BPD and C-PTSD and while there are some similarities – predominantly in terms of issues with attachment (though this plays out in different ways) and trouble regulating strong emotional affects – the disorders are different in nature.
This symptom is neither included in the diagnosis of dissociative disorder nor in that of PTSD in the current DSM-5 (2013). Individuals with Complex PTSD also demonstrate lasting personality disturbances with a significant risk of revictimization.Six clusters of symptoms have been suggested for diagnosis of C-PTSD:
Alterations in regulation of affect and impulses
Alterations in attention or consciousness
Alterations in self-perception
Alterations in relations with others
Somatization
Alterations in systems of meaningExperiences in these areas may include:: 199–122 
Changes in emotional regulation, including experiences such as persistent dysphoria, chronic suicidal preoccupation, self-injury, explosive or extremely inhibited anger (may alternate), and compulsive or extremely inhibited sexuality (may alternate). Variations in consciousness, such as amnesia or improved recall for traumatic events, episodes of dissociation, depersonalization/derealization, and reliving experiences (either in the form of intrusive PTSD symptoms or in ruminative preoccupation). Changes in self-perception, such as a sense of helplessness or paralysis of initiative, shame, guilt and self-blame, a sense of defilement or stigma, and a sense of being completely different from other human beings (may include a sense of specialness, utter aloneness, a belief that no other person can understand, or a feeling of nonhuman identity). Varied changes in perception of the perpetrators, such as a preoccupation with the relationship with a perpetrator (including a preoccupation with revenge), an unrealistic attribution of total power to a perpetrator (though the individuals assessment may be more realistic than the clinicians), idealization or paradoxical gratitude, a sense of a special or supernatural relationship with a perpetrator, and acceptance of a perpetrators belief system or rationalizations.