Could your family move past this?

It’s horrible for you to witness this and feel so powerless and angry on your sister’s behalf, but until she can really see and acknowledge his behaviour for what it is, and is ready to take steps to get away from him, then you can’t really confront him or cut him off. All that will do is lead to him isolating and punishing her even more, and exacerbate whatever toxic dynamic goes on behind closed doors.

As you’ve said, the best idea is to talk to her alone and let her know you’re unconditionally there for her, if and when she needs you. But be prepared for her to get defensive or push away any notion of abuse. She’ll have become acclimatised to his behaviour like the proverbial boiled frog and will have normalised it in her own mind and become an expert at excusing, minimising and explaining it away - truly seeing it for what it is can be incredibly painful because one of the overwhelming emotions once the scales drop away is often shame.

Coming from the kind of background you describe may make it even harder for her to identify and understand her situation. But at least you’ve got her back and can keep a watching eye on her, difficult as it is to stand by when he’s pulling this kind of shit in front of you.

Posted too soon.

In your case it sounds like you think your sister may be in an abusive relationship - talking to her privately is the first step.

If your sister is in an abusive relationship she needs you to keep interacting with BiL and otherwise being there for her as the very worst thing for her would be to be isolated from those who do love her.

I had an ex who was an appalling passenger.

Its very much the mirror image of your situation but despite holding a driving licence she had no idea how to 'behave' in the car as a passenger, shouting at me, having rows, back seat driving etc.

I think that I should have said long ago that either she shut up in the car or don't travel with me.

A slap in those circumstances without the the anger I don't think would register. But the anger would paint him in a very bad light in my family with or without the slap. Moving past it would probably depend on how typical it was.

Agree.

Depends what your sister thought.

My husband and I would probably whack eachothers hands out the way if we were messing with eachothers cars and it annoyed us.

You could say you thought it was a bit vicious and ask her more about it.

To play devils advocate, if someone was faffing with the console and blocking my view, and I’d maybe not seen a car coming and got a shock or whatever I could see myself slapping a hand away or shouting.

But the actual specific incident doesn’t matter. It seems like there’s a lot of back story and a lot going on, so it’s the whole picture you should be acting on not trying to pick a single incident. And it does sound like there’s a problem.

That sounds very sensible.

Children who witness DV are more likely to be abused or become an abuser in their adult lives. In your sister's case, DV has been normalised for her. It'll make it even harder for her to realise she's in an abusive marriage and that this isn't normal.

Same thing happened to me. My first husband was terribly violent towards me and I thought it was normal because I got beat by my parents and siblings as a child. Took me years to have enough and leave him.

He’s an evil Controlling prick and you need to help your sister get away form him. He will get worse.

Can you speak to your sister alone and express your concern? I wouldn't stop interaction with him as this will just make it easier for him to isolate your sister from her family and friends.

Let your sister know that you'll always be there for her and if she needs support, emotionally or physically, then you are there for her.

If she leaves him or tells you she wants to, let her stay with you. Don't turn her away. Then help her rebuild her life.

Why are you second guessing yourself?

I'd not say anything at the time. He is driving. That puts him in power. Risk of agravting him is too great.
But also if he is getting that angry and stressed when driving (which isn't a particularly stressful thing to do...) then I'd be guessing his coping mechanisms aren't that great.

Does your sister change around him?... Yes... Just seen your update.

I'd hate him too.

He must have her where he wants her. Sadly it can take extremes for people to build up to get out of situations they shouldn’t be in.

It depends if you are willing to rock the boat. If your sister needs protecting the whole family should be rallying to it. Mumsnet doesn’t need to tell you to allow domestic abuse

Absolutely not. Unless it was to ask him why he was still there. DV enrages me to the point i don’t care who the man is I will say something.
I saw a man pull his partners hair while I was driving past them out of the corner of my eye. My son looked at me at the same time and we both questioned what just happened. I reversed back down the road and asked her if she was ok. He spoke 3 times saying he slapped her bum playing and she laughed awkwardly. I didn’t want to press it and make it worse for her that night so I went home and downloaded the car dash cam footage. We watched it over and over to make sure we were correct with what we saw. I found out which house it was and reported it. Haven’t seen him for months.

I would ask her but I find driving quite stressful and someone messing about with the radio would probably irritate me, although I wouldn't slap them
I wouldn't stop interacting with him based on one incident it would depend on what his behaviour is like the rest of the time. Abuser's are usually very careful so it may not be that.

Definitely reporting to the police on the non emergency number op.

I would have had asked him what the fuck does he think he is doing to my sister and has he lost his ever loving mind.