is this not unfair?

I am 15 years old and my 41 year old half brother (A) still lives in the house. My dad is 68 and is constantly disrespected and screamed at by A.

I feel bad for saying this but my dad is a SEVERE pushover and always accepts it, but if I did the same thing (I'd never) my parents would disown me. No one wants A in the house anymore considering he is a grown ass abusive, unhinged man, but my dad is not doing anything about it.

A has said some horrible things, exhibit A being him threatening to off all of us multiple, multiple times and saying he will only leave the house when our dad dies. That is only about 1% of the things he has said/done. Also A lives in our living room and has his own bedroom, so we can never ever have anyone over or go anywhere but our rooms. He also acts like a bratty toddler and claims this is "his house" or "his childhood home".

My dad still continues to give him money and makes him orange juice everyday and leaves it in the entire shelf that A has dedicated for himself in the fridge. My dad has given him enough money to leave the house. A steals food from us everyday. A claims he is looking for a place and says he will leave but coincidentally has 1000 different health issues and says if he leaves, he will be leaving all of his things here.

When I have a go at my dad for A still being here my mum gets so angry at me since my dad is just an old man but he still has his awareness. I feel bad for shouting but it is such a depressing environment to grow up in. My dad just keeps giving him whatever he wants and A shouts at him daily. Call me what you want but I really hate my dad for this.

What can I do?