I like looking at the betting odds.
LINK:
Royal baby name? 500-to-1 odds on 'Macbeth' - Money - TODAY.com
10/1 are the names Victoria, Mary, Elizabeth. Coming in second at 12/1 are Charlotte and Alexandra. I am partial to Charlotte (and Alexandra). BTW Diana is 25/1.
For boys names the lead at 10/1 is Philip, followed second at 12/1 with Arthur and Charles.
Looking at the above I think we're coming into a popular time for the name Charlotte, so I'm going to go with the three names: Charlotte, Alexandra, Elizabeth, in whatever order.
For boys I think Philip is almost a dead certainty, so would go with Philip Arthur Charles as a nice gesture.