First of all, it is important to understand that narcissistic personality disorder is a real diagnosis made by a specialist.
It is clear that such parents can have a bad influence on their children.
The narcissist needs admiration and unlimited attention from others.
Such people suffer from low self-esteem and any criticism deeply hurts them, causing a feeling of shame.
To separate from your mother without severe pain, you need to develop a healthy sense of self and adequate self-esteem.
If parents can understand their diagnosis and condition, then their job is to show empathy, set personal boundaries, and monitor mood swings.
Unfortunately, psychological work will need to be done with a child whose parents suffer from NPD so that he realizes that it is not his fault that the parent behaves this way.
Earlier we wrote about how to discourage a person from being rude.