Just want to cut all ties

My upbringing wasn't too great my parents would hit me for something as small as laughing (from the UK so not legal or normal) they would make me and my sibling go park alone from ages 4/5 and 6/7 then when we returned they had gone out and left us and we had to either climb through a window or go to our neighbours and ask to stay there until our parents came back usually hours later. My older brother would have to get up with me throughout the night from the age of about 10 I was around 2 (my sibling told me this and I remember it from around 4+)

It wasn't until a few months ago I realised how bad my parents were and still are they are forever putting me in the middle of situations ( asking me to keep secrets from my siblings or from the other parent)

Never there to support or help me , I asked them to watch my children in 2018 so I could have movements checked during my pregnancy, they told me they had plans and were going out so no. Luckily my sil had the kids and I went hospital I found out my baby had passed my parents insisted then on coming to the hospital I said no I didn't want them to but they ignored me and came anyway.

I've had to quit my job because my mum said she'd help with childcare but then kept lying saying she had other things on and couldn't (I caught her in the lies) and now I'm pregnant again and I asked her if she could arrange her day off to be when I go in hospital (c section so definite date is known) and she tried to say she couldn't do that but she is doing it for when my sister has her baby next month. When I said that to her she reluctantly agreed but went straight to my sister moaning about having to do it for me. Yes I know I got pregnant and it's not her responsibility to help me when I'm the one that got pregnant but it hurts she is so reluctant to help she only works 2 hours a day so it's not difficult to switch shifts with someone.

This is only a small portion of how they are but I just feel like I want to cut all ties but how do I when I have kids who want a relationship with their grandparents