I have always known that BIL has aggressive tendencies, I've seen the way he sometimes berates my sister and how aggressive, condescending and angry he can be. My sister has been in tears at times, but she has never actually opened up to me, and any suggestion that her DH might have abusive tendencies is met with anger.
Yesterday, I was spending time with my 10 year old niece. She told me, that a couple of days prior, she was in the car with BIL, her 1 year old sibling and my sister. They'd been arguing, BIL was shouting at my sister and out of anger, swerved the car, it skidded all over the road, he then stormed into the house slamming the door behind him. My 10 year old niece was laughing whilst telling the story. I asked her if anyone in the car screamed or was scared and she said they all did and were.
I told this story to my mum, who made excuses for his abusive behaviour. She refuses to even call it abuse or abusive, she's an apologist because my own dad was very aggressive. She said his behaviour was terrible, but that abuse is subjective, and everyone gets angry and loses it sometimes. When I point out that he could be arrested for dangerous driving and that intimidating your wife and children most definitely is abuse, she asks 'why I want to label everything as abusive.'
I've done a lot of internal work to accept that elements of my childhood were abusive. It's taken a lot to recognise and understand that what I experienced (and the situation my sister is in) is not normal. Healthy relationships don't include the above. I really just don't know what to do this, I feel like I am the only one in my family who finds this behaviour abhorrent. I can't talk to my sister or my mum. I am worried about the impact this will have on my niece / her sibling.