Ok, here I go
They named their first one George (tradition) Alexander (not out of tradition, but mostly because they like it I suppose) Louis (one of William's names who honours some one that I can't recall right now).
I'm not a british royal family name expert like some of you beautifuly are (I can't get enough of the many listings, names' histories) but my guess is that they might choose a combination of the following ones:
GIRL: Victoria (Charles is said to like the name and W&K might take his advice),
Charlotte
Alice (very traditional)
Mary (very traditional and so beautiful IMO)
Alexandra
Elisabeth (so obvious)
Margareth (why not?)
they can surprise us with some "out of the box" name but I don't think they'd choose something like Kayla (trend & fashion
). They'd go for Emily or something like that, more traditional.
As for the name Diana, I can see they choosing it if they both like the name. I don't think William would not choose it because of it's package or whatever, it's his late mother's name and he should use it if they like. I love my late mother but I wouldn't use her name for my daughter as I don't like it
BOY
Arthur (one of William's names as they did with Louis for George)
Michael (obvious)
David
Philip
Charles (ohh little prince Charlie... unlikely, but it would be adorable)
Leopold (very old but who knows
)
Albert (not my first choice, I don't like it)
If they don't use any royal name, they might choose something like Anthony. Some of you have said Jonathon and I absolutely love it!
It would be AWESOME if it was a girl named
CAROLINE My name was CarolinA (not with "E") before I born untill my mother found out that the Prince of Monaco's daughter name was CAROLINE so I was named after Princess Caroline of Monaco and I'm very proud of it
Kate's mother name is Carole, so almost there
of course this is my guesses, not that they could have other things in mind...
Oh well done! 
Now that would be a musical name: Princess Penelope. (The name always reminds me of the word calliope. I have very fond memories of a calliope, played at a amusement park my family visited when I was young).
Followed by a distant James at 20/1. If it must be either I say go for James. Henry, Philipp and William make no sense showing up in the list (I call that sand-bagging) given there are three living breathing examples of each current in the BRF. Albert would be acceptable but at 25/1 it's a question, though there are a staggering twenty-six (26) names coming in at 25/1 odds.
Elvis is 1,000/1. Joffrey is kinda cute. (500/1). Wouldn't the English spelling be Geoffrey? Now that sounds very classy: Prince Geoffrey. I like it. Has a modern ring as well as having antecedents.
(it honors myself, of course)
