The first thing I want to do is to frame your question properly. This isn’t a psychological question. This isn’t about dealing with narcissists, or an ex-lover, or a blended family debacle. This is a legal issue. Often times, psychology and law overlap. When it does I defer and suggest legal advice.
I highly recommend you begin thinking about this as a legal problem — not a problem with narcissistic parents, psychologically wayward half-siblings, or annoying stepchildren. At that level, you will likely find continued frustration as their system isn’t set up to be open to discussion or change. You don’t want to go in armed with psychological advice and understanding. You’ll want to show up with real power to make a change. This will require a legal opinion and advice.
The reason I am advocating this is that this isn’t about a child being treated poorly. To use your words, what is happening is nothing short of “attacks and abuse.” If you were told by a friend of yours that on a walk in the park they were attacked and abused — how would you react? You’d tell them to go to the police — your answer would be a legal one. If they told you they were annoyed by someone in the park you’d have options to offer about what to do. Your child is being attacked and abused, the response needs to be legal — not philosophical. The moment a situation is labeled as abuse you need to shift from psychological to legal. I would not think these are circumstances you’ll want to deal with from a psychological perspective.
I encourage you to get legal advice from a family and/or divorce lawyer. Explain that when your child goes there to visit he or she is at risk of being abused. I’ve had to make this recommendation to my clients regularly. The result is that it is using the system that is requiring visitation to protect your child is better than trying to manage the situation psychologically. Visitation should not put your child at risk.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral