My mother refuses to talk to my brother

My mother refuses to talk to my brotherCategory: QuestionsMy mother refuses to talk to my brother
Alicia asked 2 years ago

Hi there, 
My mother has “disowned” my brother and has said that he is “dead to her” mainly because of his relationship with his girlfriend. He had kept his relationship hidden for about a year until she found out. She was hurt because he had “lied” about being with her, and that the girl he was with wasn’t to the standard of what she wanted for our family. My father had recently passed around the time my mother disowned my brother, and so she felt betrayed from him cause he chose his girlfriend instead of his family. 

My question is, is it islamically right to disown your son because of the person he is with? And the stuff he has done (ie drinking, hidden relationship)

Some more context to this story, when my mom and brother had gotten into it about his girlfriend, he had said some things to her like “she isn’t his real mom (his mom was from my dads first marriage, but my mom had raised him since he was 1yr old), that she was Controlling, a liar, and that she would put him down. 

Now she found out that he has been married to this girl since 2018 ( that would be the year she had “disowned” him). She had told me to cut ties with him too, but I don’t feel like that’s right since he is my biological brother. 
Is it right to disown him because of “him choosing that girl over his religion and family?” What should she do?