Advice for my brother

My brother is in a very touch situation. I already gave him my opinion but I would like some people's opinions that don't know me. My brother and his wife have a 2 year old. He also has my nephew from another women. He's 11 and he's had full custody of him since he was 3. My brothers wife has been really the only mother figure in his life. My nephew and my brothers wife got into an argument because ig he had been feeling left out and feels like everyone only cares about his little sister and my brothers wife ended up telling him "Because she's my real child! You're not!" So my nephew started crying and my brother and his wife started fighting and she's refusing to apologize and saying out loud for my nephew to here that is she supposed to lie and it's impossible for someone to love a child who isn't biologically there's as much as their own. Lie. I have 2 bio kids and one adopted. Love them the same. But even if you feel that way, don't say it IN FRONT of the kid. I gave my brother my opinion. But I would like yours

Edit: I personally don't know how their relationship was before. My brother is in Canada sadly I don't get to see my nephew often accept for FaceTime so idk if this is new or if the relationship was strained. I do know he did love her as a mother figure so it hurt him.