We have new neighbours (moved in a few months ago). They seemed nice and decent enough but over time, we started to hear shouting and swearing. They have a daughter around the same age as my children so they always play together outside, they get on really well. The thing is, a few weeks back there was a really loud row in the middle of the night, and the police was called. All I know is that the next day a policeman came to ours to ask what we know about them and when I asked her if it's safe for my kids to go to theirs and play, she said it's fine during the day but she wouldn't encourage sleepovers as "some things happen there at night". I didn't ask what, not my business and that's all I needed anyway. We were also told to call the police if we hear any noise like doors banging... After a few such incidents (shouting and screaming etc always at night) we now know that they drink and become quite violent, both parents. I let my kids play with their girl outside but I say no to sleepovers. Now my other neigbour (who isn't aware of all of this as they live a few houses down) always allows her daughter to have a sleepover there. This poses two problems for me: 1/ My children think I'm just saying no without reason, I can't possibly tell them why - but I can handle this, as I know I'm doing the right thing. 2/ Should I tell my other neighbour that it might not be safe (we're not close friends, but we talk occasionally about kids/weather etc)? On the one hand, it's surely not my place + I don't want to ruin their daughter's friendships, she shouldn't have to pay for her parents horrible behaviour, she's actually a nice kid; on the other hand, what if, God forbid, something happens and then I would never be able to forgive myself.
Now that I wrote all of it down, i'm thinking I might be overthinking the whole thing 
but I'd like to hear other opinions please.
(Just to add, it doesn't look like the social services are involved or anything)