I hope your Grandparents nevertheless have a nice anniversary - as a parent I can certainly understand why even after 6 years they are not in the mood for a party.
Missing him is natural - if you didn't there would be something wrong, and he certainly remains missed here!
All of the very best for the weekend and I hope you all don't find it too hard because as I remember C5 he much preferred to have a good time - as I remember from watching this video:
http://www.youtube.com/watch?v=xL8lJKNIuhI