I can utterly empathise with you here. My grandmother was exactly the same with her children (my mother), and grand children. She would fake heart attack s and fainting spells, migraines and all that. Until none of us could stand it anymore.
My mother nursed her in the final months and I know she felt very much as you do. She often used to have to walk out into the garden an tell at the sky.
As for me, I couldn't go back and see her because i just knew that I would have said something I couldn't take back.
Years later I still feel I made the right choice. Good luck and I wish you all the best . Look for respite to give u some reprieve.