I have the same and I am usually the one never joined in on the arguing and the calm one. I have usually just sitten around breakfest watching netflix hearing them screaming at each other for years hoping for a divorce and my brother not to mention 28 still lives at home.

Although yesterday I lost it and I got into a brawl with my brother and even tho he was the one who started the brawl i started arguin but also tried to end it with something that should have (i got calm) then he just got cocky and I wanted to put him in his place. Obviously my mom took his side cause she is overprotective of him (lives at home 28 years, handles his economy, has been bullied for having tantrums) he doesnt understand that even tho im 9 years younger im almost 20 now and he is not "the big bad brother" who can do whatever he wants and acts like he supports our family.