Your JW parents should NEVER be permitted to have access to your children while at the same time they actively shun you.
It sets a terrible example for your children to see you being disrespected by your own parents - let's face it, shunning (being treated like you don't exist) is the ultimate form of disrespect - so unless your JW parents are prepared to behave like normal human beings, they should NEVER be allowed to have access to your children. Frankly, I have come to the conclusion that for as long as my JW parents remain JWs, it is psychologically abusive to allow my children to be exposed to their grandparents' disrespectful behaviour.
The only times they've seen my kids in the last 15 years have been when other non-JW relatives are present. They go out of their way to appear as normal as possible in front of the non-JW relatives and they wouldn't dare attempt to shun me or Mr Scully in their presence. They don't want to Bring Reproach on Jehovah™ by being an honest representation of how JWs really act. I think they're actually embarrassed by the possibility of having to be strict with the rules in front of non-JW relatives.