OP,
My condolences to you on the loss of your father.
Please listen to your body, which is clearly your gut screaming at you to back away.
Your mother is a horror and always has been.
Your father has past and your obligations are over.
Your obligation NOW is to YOUR children.
By being a stressed out mother from running around after your poisonous mother, you will fail YOUR children.
You sound like a lovely woman who has suffered hugely during her childhood and now your father has died, continuing to feel caught in your mothers toxic web.
I cannot stress how much you need to focus your feelings of responsibility towards your children.
Your children deserve a mum who is in good MH, can focus on them, and enjoy them.
You owe your mother NOTHING.
However, you owe your children the best childhood you can give them.
You sound MUCH too kind and giving to do it for yourself, but,.... if you rightly frame it in the best interests of your children, perhaps you can find the strength to step away from this woman who has caused you so much grief.
You cannot be your best self enduring the stress that you are carrying.
Try and take some time to reflect on the legacy of your parents marriage, and their legacy of the childhood YOU have had.
Reflect honestly on the woman you are as a result of this childhood.
Now, reflect on what you want for YOUR children.
I have NO doubt that you are a mother who wants the best childhood for her children, certainly better than YOU had.
Think about how you want them to remember you and their childhood.
Writing all of this down is very, very helpful.
If you do this, I think it might give you some clarity.
Keep posting.