What rights would they be trying to change, I wonder? I do agree that if the parent is unfit then the grandparents should be considered for custody if they would be fit to take on the child. But if the parent has legal custody, as Casey did, the grandparents can't just waltz in and take the child, even if it would be better for the child. If the A's are thinking they should just have been able to take Caylee away from Casey with no involvement from the courts, well, there's never gonna be a law that allows that.
IMO Cindy seemed pretty worried in that Myspace post. The gist was basically, "Who is taking care of Caylee since I've always been the one to do it and now she's just out there alone with her irresponsible mother?" I do think they probably didn't realize just how bad it could be, but OTOH they had to be pretty suspicious once a couple of weeks had passed and Casey was still giving them excuses not to see Caylee, excuses they had to know were lies. They had to know there was no nanny, no car accident, etc. They probably never imagined that Casey would hurt her, but they had to be worried about what was really going on and if Caylee was being tended to, fed, clothed, protected.