I am truly sorry to hear of your loss. I have lost a lot of family, including all of my grandparents. Focusing on as many fond memories of those I have lost helps me work through the pain. Permit yourself the right to grieve... and do it. I also hold on to the hope that perhaps one day, I will be granted the pleasure and joy of seeing them again.
As for your parents, they may come to some realizations, especially as they age. I know my father, an MS, is experiencing some 'truths' of his own. Dedicating your life to God the way the JWs do means neglecting most other areas of life, including non-JW family. One day, they will wake up and they will be old and no longer able to perform to the JWs (as well as their own) standards. My father misses his son and his grandchildren. He also beats himself up mentally/emotionally for not doing more regarding FS.
Give yourself time to work through your feelings. When you are ready, take your sadness and anger and place them where they don't interfere with your own principles. Use them constructively. If you feel you can effectively communicate your feelings without anger or malice towards your parents, then do so. They may also need some time to work things through. You may wish to express your concern for their well-being. Everyone grieves differently. Maybe see how they're feeling about her passing.
I have had to do these things with my father. (Sorry for the lengthiness but wanted to let you know that you're not alone.) Heaven
