How do I help my Cancer brother?

Well, to make it short, my Cancer brother got into a huge fight with my dad. I have never seen him this angry at anyone ever before, except for those times when he's snappy but that doesn't last for long. My/our dad was being a jerk, has been that way for a long time and has done things which still affect us to this day (it affects everyone and I mean deeply, not just on the surface. My brother was trying to confront him about that, to do an intervene and explain his own feelings, kind of like a "this is how you make me feel". But I could sense he was pissed on e inside. Then when our father flew into an uncontrollable rage, my bother fought back and rightfully so. It was scary, id never seen him this amgry. I'm just not sure how to make things better between them or at least how to cheer up my brother from all the ugliness and injustice that happens all too often with he and his dad. Cancer, I noticed, never really gets mad but this time he was pissed of as fuck.

You don't want to get involved yes Cancers angry I know I do, I handle things on my own I don't need anybody getting involved. Yes I do surprise people when I get angry my gentle demeanor disappears, it takes quite a bit to get me angry.