This is much bigger than, “What should I do about my pension?”
You’ve said that one of your children won’t be able to live independently. Do they lack capacity? If they do, you may want to start looking at becoming their Welfare Deputy, if you haven’t already?
If your wish is for them to live with you - for as long as you can manage, then you need to be able to made that decision. Once they become an adult (if they lack capacity) then the ‘decision maker’ will be responsible for their ‘best interests’. That won’t necessarily be you, it could be social services.
I totally understand why you’re still in your marriage, unfortunately for us, a lot of marriages become a marriage of convenience, even if others can’t see what the convenience is.
After all you’ve said, I wouldn’t worry about your pension for now. It seems just getting through each week is remarkable. When your retirement is nearing maybe you’ll be in a position to contemplate divorce. Your life may be clearer for your adult children and you never know, there may be inheritance.
I wish you all the luck in the world, keep being that strong woman you clearly are, your children are lucky to have you as their mum.