That is a terrible situation to be in, I see my grandchildren at least two times a week ,we are having a sleepover they love coming here, I dont smoke around them because they have enough problems, but if my daughterinlaw layed down her laws, I am afraid I would do the same thing you are doing ,I am a proud grandma and I would be so sad if I was not a part of their life, but I wont be bullied,I hope things get better for you, but remember this shrew will be the one to answer to her kids ,why you are not part of their life.
Things won't get better.My oldest is 13, my younger ones are 6 and 2. I haven't seen any of them in 6 years. My sons won't take control, so I am deprived of my grandchildren.