Experienced a very similar situation here with the family of 4 above, that's been ongoing since I moved here.
Long story short(ish). It got so bad one time that she ended up running out of the apartment not fully dressed, screaming and crying at the top of her voice with him running down the stairs after her. Luckily, another neighbour, also from their country of origin, was able to smooth over the situation and talk to them both in their language.
I called and reported it to the Verwaltung the next morning. They said if it happened again, I should call the police and to let them (the Verwaltung) know in writing as well as a further call.
They also said they would (and I am sure did) write to the family about complaints received from various other neighbours in the apartment block regarding noise disturbances etc.
Since then, whilst he continues to raise his dang awful voice to her and the kids quite often, he seems to be mindful of when, for how long and at what intensity! Thankfully, I've not heard any accompanying hitting sounds.
Earlier this year, the Verwaltung contacted me and asked how the noise levels etc were and stressed once more to let them know in writing if things escalated again. In this way, he said it gives them "a strong case" in order to evict them. Apparently, some other of my neighbours have already done this.
Knowing how hard it can be for some people to find a place to live and because I actually like her and the kids, I said I would only do this if I ever witnessed (saw and/or heard) his being physically violent to her and the children.
One of my friends who lives on my street has actually seen him hitting the eldest child on the street and, whilst I was appalled to hear this, my only other regret is that it was not me who had seen it!