OP I'm so sorry to hear what you're going through.
From the age of 3 upwards my biological father was physically and mentally abusive to my DM. I used to spend every night wide awake with terror worrying that he might kill her. The shouting was bad, but I was always so much more afraid of the quiet. This went on for years. On particularly bad occasions the police would come and take him away for a few days, but he'd always come back as my mum was afraid of what he'd do to us if she didn't let him back in and it was easier to keep tabs on him when she knew where he was.
At the age of 6 it came to a head when my mum sought refuge in my room one night, thinking he wouldn't dream of doing anything in front of his DD. He tried to strangle her in front of me. It took many years and a lot of therapy to get rid of the flashbacks. Even now I can't stand to be around raised voices...shouting even whilst watching rugby etc. makes my blood run cold.
It took a long time to realise that it wasn't normal to try to stay awake each night to make sure your DM wasn't killed.
I'm telling you this to make you realise that no matter how unaware you think your DC are to the bigger picture I can promise they know a lot, lot more than you think and even if they haven't mentioned it to you they will undoubtedly be feeling extremely unsettled, particularly now they've seen the violence first hand.
Please speak to the police and WA and get advice on the best course of action. His rages sound like whatever meds he's on aren't necessarily working and I'd be worried for the safety of yourself and your DC's right now. As for worrying about your DP's MH, he sounds like he needs help right now so if anything, the best thing you could do is speak to the police so they can help him get the help he needs.