From where I'm standing, your mom is the one with the real problem here. She's moved in with a sorry-ass loser and put herself and her son under the control and victimization of that person and his drug-addicted brother. If Andy is the sole supporter of the finances and the household, she has brought you, a minor child, into that situation and put you at risk for whatever yelling and other abuse he's handing out. That's not a good atmosphere for her, a completely vulnerable and dependent woman, and it's especially not good for you, her child.

What prevents your mother from doing something to earn a living and support you guys without having to shack up with, and be dependent on, some controlling, loud-yelling loser? This is a situation that far too many women put themselves in. They hook up with controlling assholes and bring their vulnerable children into that picture, too. She's the one who ought to be looking at improving her lot in life, quite frankly. Doesn't sound like it'd be the worst thing in the world at all for y'all to be back with your grandparents (except, of course, she'd be moving from one dependent situation to another). This is why all women need to get as much education as possible: so they can get decent jobs, have the self-esteem that prevents them from getting into situations like your mom's, and achieve some degree of financial independence. And so they don't have to put themselves and their children in situations where they're vulnerable to the Andys of the world.