This is a REALLY tough one to answer. When the abuse is not physical, a personality disorder like NPD (narcissistic personality disorder) is a hard thing to prove.
Because a narcissist isn’t willingly going to seek therapy for self-improvement (they’re perfect, the problem is everyone else), there likely won’t be an official, clinical diagnosis.
Do, however, keep a sharp attorney, one with experience in dealing with toxic individuals, on speed dial.
The problem with proving narcissistic personality disorder in court is the time, expense, and difficulty to actually prove it.
The effort will be exhausting and expensive and, in the end, could prove futile. The family court system simply isn’t set up to deal with the sh*t-storm associated with narcissism or other personality disorders, for that matter.