Alcoholic stepdad, what should I do??

He’s been drinking every week since my mom met him 3-4 years ago and she’s doing nothing about it. He has kids who’s 10 and 12 years old and they are both well aware that he’s drinking and they have expressed to my mom that they don’t like it. We have begun to quietly make fun of him when he’s drunk because he’s so pissed and complaining about absolutely everything. My mom does that so they can get something positive out of the situation and not let it be awkward and depressing.

Last night he drank 6 beers and started screaming at my mom like 5 times all because of a board game. And he also verbally abuses his kids when he drinks. Telling them that me and my brother are better and more raised then them and complaining on everything they do, like they walk to loud or talk to loud or eat to much. Literally always picks on them for every little thing. He’s comparing his kids to my moms even though me and my brother are almost 18.

I only visit her every other weekend and I’m so done with him. I just want to scream at his face and tell him to get the fuck out and leave my mom alone forever since she don’t have the balls to do it. She has told me that she is in fact staying with him for the reason that she has no one else close to her. Her parents are dead and she has no real friends here. Me and my brother lives with my dad and it’s too far away to live with her. But that’s not a good reason for staying in a toxic relationship, she won’t listen to me or my brother and we have been telling her this since they started dating and when they got engaged. This happened with her last boyfriend, who cheated on her for the 8 years they dated and we always told her to get out of the relationship but she never listened and she told us she regretted it. But now she’s doing the exact fucking thing all over again. She’s completely wasting her time and money.

Speaking of money. He has earlier stolen money from both me and my mom to buy alcohol. He is not mean to me or my brother, he’s just very creepy and is always staring at me when I’m not looking.

I have told her so many times to leave him and she always tells me that “it’s not that easy” and that she does love him. But I know she’s lying and their relationship is not good and everyone sees it so I don’t understand what makes her so blind to see what’s happening. Please tell me what to do!