What Now?, I'm sorry for your dilemma. I've read this thread and see there are different opinions-- those emphasizing tolerance and teaching critical thinking skills; others, like you said in your OP, say their family is a package deal.
I have been in a much similar situation, except that Mr. SailAway was the "inactive" one, and I was the indoctrinated JW. My JW in-laws were shunning their son, except under the "essential family business" escape clause, they allowed him to drive 500 miles to bring us to visit them. He tried to do everything he could to accommodate us and even went to the KH with the family during those visits. In between visits my JW MIL maintained contact by letters to me and the kids. Neither my MIL or FIL to this day has initiated a phone call to our home. Until I walked away from the organization four years ago (because I refused to shun my own son), I always felt like I was in the middle, the go between between my hubby and in-laws and my kids.
I raised my kids as JWs. My daughter "respectfully declined" a "shepherding call" from an elder when she was 17 years old and never attended another meeting. My son was later DF'd. Now my in-laws shun both of them. I know for a fact that his hurts both of my children on a very deep level. Worse yet, my JW in-laws want nothing to do with my daughter's brand new baby, my beautiful grandson and their great grandson. They are shunning an innocent baby!
Once I woke up, it got more and more difficult to put up with their venomous speech and ill treatment of my husband, so I stopped writing to my MIL two years ago. I just stopped answering her letters. She no longer writes. They have no direct evidence that I left the organization. I guess we are shunning each other.
I tell you all of this, because I think that, in the end, only pain can result from your children developing a relationship with their JW grandparents. Been there, done that.
Just Sail Away