LE may be annoyed with them but they have said they have been fully cooperative. Someone else posted when this came up that no prosecuter or judge (elected in most cases) is going to want to prosecute the grandmother and grandfather of the victim. Could be a PR nightmare. Not to mention reasonable doubt standards. Unless they do something like hide evidence that could otherwise lead the police to Caylee I don't think this obstruction charge is coming. Just my opinion.
Agreed, and though I don't have a personal opinion yet as to what they did or didn't do in terms of helping Casey, I note that being "fully cooperative" doesn't mean that LE isn't or wouldn't consider them a person(s) of interest in the future and, if LE did so in the future, you're right: LE would have to have some really really smoking gun evidence, else it could be a PR nightmare.