Irish Eyes, I can only report to forum members what I was told, and that was that 'the Yorks had all been invited', and by that, I took it to mean that Andrew, too, had been included in the invitation.
To put this into context and also give you such background information as I have, although I understand that it is the York ladies who are closest to Richard Branson / Holly etc, when it comes to invitations from Richard Branson to Sarah, [i.e. for holidays/ parties etc] I have in the past been told that such invitations ALWAYS include Andrew as well, on the basis that Branson considers the Yorks as a de facto couple. It's a form of 'politeness' in the UK [and other countries as well, come to that] that unless a formal social event is a sort of 'girls only' type of social occasion [e.g Debutantes' Mothers holding what are known as 'Mums' Lunches'] you always invite both halves of a couple to a party, wedding etc not just the wife, unless the couple has separated. Now, I do know of course that Andrew and Sarah are divorced, but over the years the Yorks have holidayed together etc if you see what I mean..
My own speculation is that [at most] only Sarah and the girls would attend Holly's wedding, as I can't see Andrew going along. I was only told that 'the Yorks had been invited' - whether Sarah and the girls all attend is another matter. The girls may of course have other committments, although I am pretty sure that Sarah would probably be loathe to miss a freebie time in the sun.....
And yes, Irish Eyes, you are quite right, Necker is very private and the paparazzi can't just stalk the island with their long lenses etc but never let it be forgotten that Richard Branson is a canny person when it comes to publicity. I am sure that pictures of Holly's wedding will be released by Branson, and if the York Princesses and indeed Sarah are there, I am sure that some shots of the guests [and there are bound to be a quite a few celebrities there, anyway, I am sure - those are the sort of circles Richard Branson moves in...] will be released too. I would not even be surprised if a deal is done with 'Hello' come to that - in return for a donation to charity etc. And so, even though you are 100 per cent right about the privacy of Necker, I am fairly sure that photos of the occasion will find their way quite legitimately into the public arena. Let's see if I am right...
Hope this helps,
Alex