I worry about my little brother’s mental health//what do I do

I’m 21, my little brother will be 9 in August. He is being raised by my mom and step dad, and they are both narcissistic control freaks.

I’ll start with my mom. She actually had a affair on my dad with my step dad, but completely denies it. She has an extremely strong victim mentality, she thinks the reason all of her kids left her house was because we wanted to me spoiled by my dad (my other brother and sister do not share a dad with me) and we “sold her out”. But in reality my older brother and sister were kicked out by our stepdad and I followed suit because my mom and stepdad didn’t want to care for me or being me to school. She also tries to make me feel guilty for the boundaries I placed between us. Anytime I’m alone with her she gets extremely emotional and says she missed me and starts crying, and it makes me very uncomfortable.

On to my stepdad. He is extremely toxic. He used me as the favorite child to make my brother and sister feel bad about themselves. Called my sister the red headed step child and straight up said he’d adopt me but not her. He made fun of her acne, how she wrote her name on everything, little things to make her feel have low self esteem. He’s done other things to my older brother along those lines. He handmade a wood paddle to hit us with, he even named it. I never had a falling out with him but my sister told me he put his hands on her once and I stopped interacting with him. It’s been over 5 years since we’ve had a conversation.

My little brother is 8 and already suffers from extreme anxiety. He has anxiety over tests and storms, and my mom and stepdad are very controlling. My little brother told me they took away his Nintendo because he had a panic attack before a test. My stepdad also apparently fights with my mom in front of him, calls her fat etc. and my mom feeds into it. My little brother told me “my dad hates my mom” and when I asked how he knew that he relied “my mom told me”.

There’s a lot of stuff I left out but it’s take a novel to write it out.

I just worry so much about him. He’s not allowed to come over to my house because of my dad (he’s painted as the evil one), so I see him when he goes to my brother or sister’s. I want to talk to him but I don’t want to scare him away by me asking personal questions. I want him to see me as someone he can trust. I’m scared he might turn out like them, but if he had some sort of positive influence maybe he won’t. I’m sad that he’s all by himself, at least when my siblings and I were going through this we had each other, but he’s all alone.

Please if there’s any advice you have tell me. Specifically, are there any questions o can ask him that are psychology based, to get a feel for his mental state? Just good questions in general to ask him?