I forgot to mention something else. It happened when they were in high school. My family member once chased a much younger boy across a shopping center in broad daylight. When they caught the boy, they grabbed his arm and held onto it while kicking him repeatedly in the stomach. The boy had done something rude that didn't merit this response.

It just occurred to me it could be ODD. They are constantly angry and claim to be mistreated. Their anger grows over time. In teens and twentites they had meltdowns when I said no to them or a teacher or boss rejected their suggestions. In their 30s the meltdowns increased and now they are having 5-6 every day while doing things in their own.