It has *got* to be embarrassing to try to dance around explain to non-jw's how a grandparent could possibly not be involved in their grandchildren's lives - especially when they preach to others about how loving they and their religion is.
By having just a little interaction with the kids, she gets to retell the same story of the 30 minutes she spend with them over and over again for 6-12 months. That way she can save face among her friends and potential converts. She can also tell her JW friends how big a test of faith she endured all for the kingdom's sake.
I may be mean and jaded about this, but I would not allow unsupervised visits at all. Not so sure I'd allow supervised visits either if said grandparent would treat me cooly in my own home. It makes me uncomfortable and kids pick up on the 'vibe'.
It's a tough situation. Not sure what I would do in this situation. But boy, oh boy! From what you've told us, your parents are wackier than most. They scare me.
-Aude.