Don't blame yourself. I don't think it's your fault. If this has happened in the past, there have to be some better ways to deal with these issues like family therapy. Also, I have learned that you have to be cognizant of your own desires and values. Find a kind and gentle way to communicate to your mom about how you feel re: all this fighting. Otherwise, it will be hard to deal with conflicts when you become an adult. Constructive feedback is always more preferable than blaming and being resentful towards others.

As for your brother, maybe your mom know it's the best way to handle the situation like that at this very moment. If you are concerned that you or she has caused harm, communicate that concern to her and ask what she thinks.