Just have no idea, how to take control of my life because I've never had the opportunity.
It starts from within you - recognising that this is YOUR life, and you have the right to live your life how you want to. Find your power and confidence.
Then you recognise that the law is on your side.
You are in the UK, so you have rights. Regardless of the community or culture in which you live. No-one, not even your husband, is entitled to take away your property (jewellery), control your money that you earn, or control how you spend your time.
He cannot "take away" your children - they are old enough that the law will give them the choice of where to live if you do move out. You can just simply move out and take them, then facilitate them visiting his house on a reasonable planned regular basis. Do you drive? Can the youngest get buses alone?
Then you get advice, from Mumsnet, from colleagues, from professionals, from charities and advice services, from whoever. Don't be embarrassed to ask.
Then you decide what you actually want. Do you want to move out? Get divorced?
Is there any way to stay in the current home but essentially ignore your MIL? Can you learn to not care what she thinks and says, and just get on with your own life whilst living there? Can you answer her back if she makes comments, argue with her, tell her exactly what you think?
What is likely to happen when she passes away? Will your DH inherit the whole house?
Are you currently lined up to be her carer when she gets old? Do you want to be a carer, doing intimate cleaning, bathing, etc?
Then you make your plans and take action - either all at once, in a big show-down, or subtly and silently, playing the long-game.
Most importantly - is there any likelihood that your husband will get violent?
If you are completely sure it would never come to that, it makes your situation better, because then you don't have to fear his attempts at financial control, emotional control, manipulation of the children, or whatever else he tries on.
Just be careful - because the more you find your own power and take back control, the harder he and MIL will try to put you back in your box and keep things the way they used to be.