Prince Guillaume and Princess Sibilla were in Monaco September 10, 2009 for the second annual award ceremony of the Prince Albert II of Monaco Foundation. Here's a little info about the awards and the ceremony. There are some pictures of the regal guests on Belga. I searched Princess Astrid and Prince Lorenz of Belgium attend the Foundation award ceremony in Monaco for the pictures although I did try to link the gallery I found. I'm not sure if it will work.
This was the same day as the EORTC charity gala which Guillaume and Sibilla also attended. Princess Astrid and Prince Lorenz of Belgium were also in attendance. I didn't see Crown Princess Victoria at the award ceremony though she was at the EORTC gala.
Prince Guillaume was also at the Lycée Athénée à Luxembourg recently and gave a presentation.
I saw pictures of an event that Prince Jean attended recently but I can't locate them now, and I don't recall what the event was. I was so busy looking for state visit stuff that I was distracted.