what would you do if you suspected? - kinda long

I live in a townhouse complex, and have for the past 5 years and never had a problem. I knew everyone who lived here, and their kids and everyone got along fine. Well a few months ago a new family moved in right next door to me. The townhouses here are only 2 bedroom, and they moved a family of 6 into this house. Our walls are super super thin. I used to be able to literally hear my one neighbor go to the bathroom through the wall (and I am NOT exaggerating in any way!!!!)

Anyways, so this family moves in and all of the sudden its beyond crazy down here. Every day all I hear is screaming through the walls. Now with 4 kids aged 9 and under, I know I'm going to hear fighting and stuff, but this is completely different. This is the mother and her boyfriend fighting with each other, screaming obscentiies at the kids and just like all out battles. Well the one day the mom was at work, and the boyfriend/dad to some was watching the kids. I had the TV turned up loud as always so I dontt hear the bullshit next door, and all the sudden I hear this screaming and pounding and a little girl crying her head off. He's screaming at her for not picking up her toys (she is around 2-3 i believe) and telling her he is going to "f*ck her up if she doesnt start listening" "beat her f*ing ass if she can't do anything right" and then I hear him smacking her and her crying even louder. Then it goes quiet. Eerily quiet. I know kids just dont stop crying like that. A few hours later I hear him threatening to cut the other girls hands off if she can't keep them off his stuff. I know people joke with their kids and all, but this wasn't joking. This was full on screaming and threatening and made me physically ill to hear. Then I can hear thuds and more crying and a few more thuds and then again, absolutely nothing. So I called CYS and reported them for suspected abuse, only to find that this isn't the first time they have been reported and they were kicked out of their old place because they had 6 people & 6 dogs in a 1 bedroom and had CYS called on them multiple times.

A few weeks later, I am again watching tv with the volume up over 30 and hear him screaming at the girl again and making her repeat that she is a worthless piece of shit that no one wants or loves. This broke my heart as I can never imagine saying something like that to my daughters! Then 2 weeks ago, I hear him again screaming and then because I was on the other side of the wall he was next to, heard him hitting the child. And it went on for more than 15 minutes. So again I called. And again, they did nothing.I called the cops, and nothing. The next day he apparently found out that I called, or at least assumed it was me because I was the only one home, and has begun threatening me through the walls. That lasted a week, and has thankfully stopped. Luckily my children weren't home for that, and most of the bad incidents. But they can her him through the walls and they are TERRIFIED of him. So much so, that I have had to lay with them until they fall asleep, and have music playing semi loud in their room so they cant hear anything.

I dont want to get to involved because I have to live next door to these people and our backyard is all connected. But I am scared that something bad is going to end up happening to those kids if someone doesn't do something.