I think that if your family members are avowed violent criminals committed to attacking people based on their being a member of a group that is clearly discernible in society their confession to you of that fact should be admissible in court.
If you would please review https://news.ycombinator.com/newsguidelines.html and use the site as intended, we'd appreciate it. That means curious conversation on a diverse range of interests—not doing battle with enemies. Curiosity is the first casualty when the threads go that way.
Past explanations:
https://hn.algolia.com/?sort=byDate&dateRange=all&type=comme...
https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
The law doesn’t seem to require there be a victim, so I think that scenario would involve other laws and isn’t the intent of the law in question.