My boyfriends mom is irrational and treating him like ****. idk how to help.?

hiiii. so im 17 and my boyfriend is 16. hes in therapy for adhd and bi polar disorder. hes been doing amazingly. but, his mom thinks that arguments and fighting goes one way, shell yell and scream at him for some of the stupidest reasons, most of them for him just being a normal teenager. she threatens to send him to a group home and pretty much verbally abuses him. my boyfriend gets really depressed from this and doesnt really know what to do. his therapists are talking to his mom too and telling her that fights and problems dont go one way, and that its both of them who need to work on it...but when the therapists are there, she cuts him off and tells them shes doing everything she can and he just rebels. which i know for a fact is not true. i dont know what to do and he doesnt know what to do. help?