What should I do about my brother who I think is unstable?

He makes mean comments about my mom and calls her dumb and says he doesn’t care if she died or something happened to her. I cut him off a few years ago and later we rekindled and he said that he would kill me if I ever blocked him again.

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by the way he lives in another state. I haven’t seen him in like 5 years
What should I do about my brother who I think is unstable?
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