Emotionally and psychologically abusive

This is going to be a long one, so please bare with me. I'm 28 years old, so is my husband of two years and no, this isn't about him....it's about my dad.

My dad is extremely emotionally and psychologically abusive towards my mother and his kids (my brother and I). I moved out the house the first opportunity I got they day I wrote my last exam at 18.

My mom and him have been married for 31years. He doesn't allow her to work, he constantly lies, he can't keep a job (he's about to loose his current job after getting four warnings for smoking), he does shady deals under the table at work that gets him fired, he constantly accuses my mother of cheating on him (he even accused her of cheating on him with MY HUSBAND) even though he's the one who cheats, he pressures my mother into sex. She's also getting older and her downstairs hair is falling out a little and he accused her of shaving it for another man. She isn't allowed to come visit me because on the same day she gets here, he accuses her of cheating with my husband because she doesn't answer his texts fast enough. He will phone her constantly. She can't even visit my grandparents because he does the same thing since they live in the same town we do. She's not allowed to go out with friends just for a glass of wine or she's sleeping around. So she has no friends anymore. A few years back, my mom also almost got cancer due to HPV and he accused her of getting it from someone else. She lost her entire womb due to that. In 2016 when I had my uni graduation and my now husband and I were dating, my parents came down for it. He accused her of "looking at her daughters bf". She got angry and threw water at him and he shoved her so hard she fell. She has a really bad hip due to a car accident when they just got married. He also completely ruined my wedding day. Apparently last week he also slapped my 2 year old nephew behind the head really hard for being in front of the tv. These are just the instances off the top of my head. I've begged her to leave him but she can't support herself and she's taking care of my brother's 2year old son because he is also struggling at the moment.

So a few days ago I get a text from her that she wants out and if she could come stay with me with my nephew for a little bit. Of course I said yes. I send her money to get here. Now my dad is threatening to kill himself (not for the first time, he's done it before), trying to guilt her into going back. Hubby and I are also trying for our first baby but been struggling for two years due to me having PCOS. I just feel like everything is upside down. We're scared that he will show up here (they live in a different town about 4h away) and cause trouble. He has threatened to shoot my husband before.

I don't know what to do. I've phoned the cops but they are useless. They spoke to him and he says he's okay now to them while still after, threatening his life to my mom. I told the cops he is manipulative and a good liar because that's all he does, but they apparently can't do anything. Please, I need advice. I'm so stressed out and in the middle of a panic attack.