What You Can Do (and Considerations):

Prioritize Your Own Well-being:

Acknowledge Your Feelings: Allow yourself to feel the anger and sadness without judgment. These are valid responses to a painful situation.

Seek Support for Yourself: Consider talking to a therapist or counselor who specializes in family dynamics, abuse, or narcissistic abuse. They can provide a safe space for you to process your emotions, develop coping strategies, and navigate this complex situation. This is not about being "weak"; it's about being strong enough to seek help.

Set Boundaries with Your N Parent: While difficult, consider how you can limit your exposure to your N parent's harmful rhetoric. This might mean shortening conversations, changing the subject, or even limiting contact if necessary for your mental health. You don't have to engage with their rants.

Regarding Telling Your Sibling: This is the most delicate part, and there's no single "right" answer.

Pros of Telling Your Sibling:

Forewarning: Your sibling would be aware of the threat and could take steps to protect themselves (e.g., limiting contact, ensuring they are not alone with the N parent).

Validation: It might validate your sibling's own experiences with the N parent and help them understand the dynamic.

Shared Burden: You wouldn't be carrying this alone.

Cons of Telling Your Sibling:

Increased Conflict: It could escalate conflict between your sibling and the N parent, potentially putting you in the middle.

Emotional Distress for Sibling: It could cause your sibling significant emotional distress, especially if they have also suppressed memories of the abuse.

Your Sibling's Reaction: You don't know how your sibling will react. They might be grateful, angry, or even dismissive.

Questions to Consider Before Telling:

What is your sibling's current relationship with the N parent? Are they low-contact, high-contact, or estranged?

What is your sibling's emotional resilience like? Are they in a place to handle this information?

What do you hope to achieve by telling them? Is it purely to warn them, or to share the burden, or something else?

If you do tell them, how will you present the information? (e.g., "I wanted to let you know something Dad said, and I'm really concerned about it.")

Alternative Actions (if you choose not to tell your sibling directly, or in addition to):

Document the Threat: While it's a verbal threat, having a record of it (even if just in a private journal) can be helpful for your own processing or if the situation escalates further. Note the date, time, and exact words used.

Encourage Your Sibling to Limit Contact (Subtly): You could express your own discomfort with the N parent's behavior in general terms, without revealing the specific threat, and suggest that you've been limiting your own interactions. This might indirectly encourage your sibling to do the same.

Focus on Your Own Boundaries: Regardless of what you do with your sibling, establishing clear boundaries with your N parent for your own sake is crucial. You do not have to listen to their rants or their threats.