Thanks for all the suggestions, in the end I couldn't get things to work out, lots of time delay issues between my wife's grandmother in SoCal and her sister in Sapporo, compounded by a series of cultural issues that my wife's grandmother (I love her to death by I have to say "somewhat predictably") glossed over until it was too late. This clearly would have worked out much better if my wife had just learned to speak Japanese as a child ;-)
The irony of the whole thing is that I had offered to fly my wife's grandmother (and my wife's mother and aunt) over when we first started planning the trip in September. Nobody took us up on the offer, and then as we were preparing to leave our kids on my mother in law for the week, the trans-Pacific communications started up. We have tentative plans to go skiing in Nikseko next year, and based on this will just buy my wife's grandmother a ticket even if she again declines when we are in the planning stages.