I totally understand what you are going through 2Pink!! Although my daughter was not raised inside the world of JW's...she still sufferes the same.
My parent's are both extreemly active, and shun me obviously, as I am Da'd. Having said that the few times they see my daughter who is almost 9 they do nothing but preach at her.
They had her the other day, and she came home talking about the end of the world...when she first told me what has been discussed I freaked on her, (not her fault I know, but I was just ticked because they can't be asked seeing her any other time, and when they do they scare the crap out of her).
When I calmed down I went to her, and told her why it is that we don't go over to her grandparents house, why they don't talk to me, and why the whole relationship is a mess!! At 8, she said to me, "Mom, thats blackmail!"
I know your children are younger, but they can comprehend so much!! If you decide to let them visit their grandparents (unsupervised), all you can do is talk with them and find out what they are saying to them and work from there...if they are going to "run" you down to your children...well then there would be NO way I would allow the grandparents to continue contact with the children!
Your children will see through their tactics as they grow up, and make their own decisions based on their grandaparents actions, as long as you are open and honest with them!!
I truly hate all the "conditions"!
H4E