Does Anyone else get trigged by other people's anger?

I don't have IED but my step brother does. I'm not sure if it's an IED thing that happened today, I'm not well familiar with this disorder, and I'm trying to learn more. There was altercation this morning. My dad got mad at my bf. And they got into an argument, to the point my dad thought it was okay to get physical. (He has his own issues but doesn't "believe" in therapy), my step brother, despite the conversation at hand not being about him, got angry, and physically aggressive with my bf. We had to pull him off of him, he went after him as my bf was leaving to calm down.

After my bf left, he threatened to break his things, and I put his things up in time. He also has autism and does hyperfixate on playing video games, so I used that as a distraction and to calm him down. And he had forgotten about breaking things.

Which goes into my question at hand. Does anyone else get angry when those you love and care for are angry at someone/something? If so, what helps you cope through this?