Beatrice and Eugenie are Charles's nieces, whereas Archie and Lili are his grandchildren. I would expect them to be treated differently.

If the Californians do attend, it's possible Charles would want a photo of himself and Camilla with all his descendants, and the photo may or may not be released to the media. I doubt he will want a photo of himself with his nieces and nephews.

I'm hoping for a photo of Charles, William, and George. It's been a while since we've had a line of succession photo.