So let me start by saying my folks have been remarkably supportive of our unschooling choices, but then they are generally remarkably supportive people - which is one of the many reasons that I consider myself the luckiest man alive.
That said, the issue of unsupportive grandparents/relatives/whatevers rears it's head on unschooling sites and posts with frightening regularity, so I've given the matter a great deal of thought over the past few years. It came up again on the SSUDs group last week, and I thought I'd share my take on how to deal with "unsupportive" relatives.
We have found that many "unsupporting" people aren't unsupportive maliciously; for the most part, they just really want to connect with the child but find that the traditional routes to connection ("What grade are you in?", "What are you learning?") are now closed. If you think about it, most of us (and a number of preceding generations) were raised and "schooled' in some basics - naming Presidents and state capitols, knowing the dates of wars, The Mayflower, yada yada. While these are all trivial pursuits, they do give us a common frame of reference, a connection point, that allows us entry into deeper conversation. Most of us were raised that way, for good or bad, and continue to work that way today.
Grandparents are no different; they are using their tried and true methods for connecting. The problem is that our kids don't know the answers to these trivial questions, don't know what they've "learned" in a day, etc. So rather than acknowledge that they need to find a different way to connect (which means undoing years of programming), our relatives will ask our children to change so they can connect. And if that doesn't work, they'll question unschooling in an effort to get us to change, all so that they can connect with our kids. This paradigm holds a very might sway.
But at it's heart, I think that most time this behavior comes from a place of good (trying to connect) rather than a place of bad. So we try to help them find other ways to connect - suggesting questions the grandparents can ask that will lead to enjoyable conversations, providing background info on our children's interests rather than on unschooling, and ensuring they get up-to-date info on what our kids are into at that particular point in time. The goal of this is simple - I don't need my parents to "get" unschooling, I need them to "get" their grandkids. Once that happens, a lot of the worry melts away - - -and many of the criticisms with it, because they no longer have a problem to solve.