[Solved] Separating from mother who has abused the children

I'm looking for some advice on what I should do for the situation I'm currently in please.

Basically, my marriage has completely broken down in the last couple of weeks and it appears inevitable that we will be separating. I have 3 step children and we have a 3 year old daughter together. We have been in a relationship for nearly 7 years and married for nearly 5.

The main issue is that I have concerns about how my wife treats the children. Around 2 years ago, my wife had a very angry outburst at me over something she wanted to buy, which I suggested we didn't need, and shouted that she wanted a divorce in front of all the children. She left the room before storming back in to throw both her engagement and wedding rings at me. I was sat down on a chair with our then 1 year old daughter on my lap. One of the rings hit our daughter, the other hit me on the head. Shortly after, I spoke with my 3 step children, who were 11, 8 & 6 at the time, about whether they had experienced anything like that before. They proceeded to tell me about incidents including: throwing a chair at one of them; smacking one of them for falling off a swing; smacking our 1 year old daughter when she makes it difficult for her to change her nappy; slapping one of them in the face and throttling them. They also talked about how bad a temper she has. This conversation was caught on our home security camera. Most of what the children had informed me was unknown to me at that time and I believe happened before I met my wife. I notified social services via NSPCC and had discussions with them about removing my daughter from the home, which they told me I should consider doing. During the course of the days after, my wife showed a great remorse for what had happened and she wanted to try and fix things and improve the situation. I spoke with social services about what I should do and they said that if I feel I can be a protective force for the children then they would be happy to close the case. As such, the case was closed and my wife and I went about repairing the relationship and improving family matters.

Unfortunately during the course of 2019, there were further incidents that I either witnessed or was told about: she slapped my then 10 year old stepson in the face for making them late for a school trip because he hadn't tied his shoe laces (this was caught on the security camera); she repeatedly hit/slapped my then 7 year old step daughter around the head and face because she had taken a pair of hairdressing scissors that she needed (I witnessed this after it had started and told her to stop immediately before comforting my step daughter); she pulled my now 8 year old step daughter by the hair from one room to another in order to brush her hair (witnessed). All of the above recent events put a strain on my feelings toward my wife and thus the relationship has broken down.

Over the last couple of weeks or so I have been checking through recent camera recordings and found other incidents including: roughness when brushing our daughter's hair/putting on her coat; smacking; giving instruction for one child to "kill" another in a very serious tone and a general lack of attention shown to the children, especially our daughter, in favour of sleeping or looking at her phone. Our daughter has some speech and language delays which I feel may be down to the lack of attention she gets from Mum when I'm working.

I haven't reported any of the subsequent incidents to social services as I was very much still of the feeling that I should remain as a protector for the children and I'd like some advice on what the appropriate steps to take are.

I have taken some legal advice and been told that we need to try to agree a separation plan that includes a plan for our daughter. This is proving to be very difficult as she is refusing to talk to me about the situation whenever I ask to, mostly because she's going out all the time (she's spent only about 4/5 evenings at home since 3/01, although she does work 3 night shifts a week, although she doesn't work through the night and gets paid to sleep). This is also having an effect on the children and our daughter and my step daughter have both made it clear that they are upset they don't see their Mum enough. I also believe she has already met someone else, and already introduced him to the children, before we've even had a chance to officially discuss the status and the future of our marriage, which gives you an indication of the way she often puts herself before anyone else.

I think it's vital that our daughter grows up knowing both parents and I absolutely want her to have safe and regular contact with her mother, but at the moment I have real concerns over how she would be affected without my wife first getting help for her issues. I would absolutely be open to a 50/50 shared agreement for our daughter's care once she can show herself to have put her issues behind her. I obviously share the same concerns for my step children too, but unfortunately do not have any parental responsibility for them. I do not believe any of the children are in any immediate danger and I have no doubt my wife loves them all very much. My concern is for their long term happiness and well-being.

When it comes to trying to agree things with my wife, I envisage her not wanting to agree to my proposed future care of our daughter as she is very likely to get very defensive about her treatment of the children when I raise it as a concern. This leaves me wondering what the next steps should be if we can't agree.

I hope you are able to give me advice on what I should be doing in this situation and whether trying to amicably agree things with my wife is the correct path to take. Also, if we can't agree, what steps I should then take?

Any help or advice would be greatly appreciated in this matter.