Cousin is in an abusive relationship and has a 4 year old with the abuser

My cousin met a guy on tinder in 2020 and had a baby with him. After about a year his mask started to come off and he is so verbally and emotionally abusive to her all of the time for no reason. He starts fights about really weird trivial things constantly purely to make my cousin feel crazy, and he does it in front of the whole family. His own entire family has warned my cousin that there is something wrong with him and that they'd be willing to help her if she needed to escape. All of her friends have said the same. He fights in front of the baby, has driven drunk with the baby, punched a hole in the wall, and recently at a wedding my cousin passed out and woke up with a black eye and a huge bruise on her arm while he was driving her home. She says that she isn't sure what happened while she was passed out but that she can't rule out that he didn't give her the black eye. He has a history of suicidal acts and is taking a lot of different mental health medications that cause him to act like he is on meth. He, to my knowledge, has never physically assaulted her, but I don't know what he would do if she left him and took his kid from him. She wants to, and she comes to our house to get away from him often. She does all kinds of stuff to get away from him. We had an intervention with her last night because he showed up to pick the baby up and immediately started fighting with her about something as trivial as his to-go order, and when she asked where he got the food, he loudly said in front of all of us (including the baby) "The titty bar. " and then did a smarmy smile at her. She thought he was joking at first and then he was like nope I really went to twin peaks, the titty bar. We were all so extremely uncomfortable that I had to go to another room because I started to have a panic attack and was trying to avoid screaming at him because I am trying to solve this issue slowly and quietly so he doesnt go crazy and hurt her. I have no idea when to tell the authorities, I have no idea what I can even say to them because he hasn't been proven to physically hurt her but he does punch walls and is scary to all of us. Are there any help or resources you guys could show me to get a restraining order or full custody? And also advice on carrying this out without causing him to go crazy and hurt her? Should we secretly record him? I want some kind of proof but I am terrified of him finding out that she is planning on leaving him.