Rant/vent about my older stupid nazi brother

So my whole family are christians and like back in april I found out my 18 year old brother (19 now) was a self proclaimed nazi.

I found out cause he kept bringing up hitler for some reason and I jokingly asked if he was a nazi and he said yes and that he was 'fully serious and a jew hater' and then I spent like an hour going off on him and more of so questioning why tf hes a nazi, and he just brushed me off and ever since then I have tired my best to distance myself away from him (we live in the same house) 

And now he keeps making antisemitic comments just to piss me off and finds it amusing when I do (we've already gotten in like three fist fights because of these comments)

I told my mom about this and explaining the conversation I had with him and omfg she was like 'well that is just whats online' and making excuses for him and shit and I generally feel like Im losing my mind the more time I spend with these bigots

If I ever found out my kid was a nazi I would immediately talk to them about it and sign them up for counseling.