I believe the entire royal family is going. Could be wrong though.
There are a few we can rule out. Meghan is unlikely to attend having just given birth. Sophie is in Kent doing an engagement so we can rule her out and I can’t see Harry going as he’ll be with Meghan (I could be wrong though...)
I am not sure the Duke of Kent will be attending as he has two engagements in Athens on the 18th and more on the 19th and 20th. Given the time difference between London and Athens I am not sure he could realistically attend a midday wedding in London (Windsor) and then fly to Athens and lay a wreath and visit a naval ship (possible of course but not all would be done in daylight).
Seems strange to arrange for this visit to be this weekend (or at least for the scheduled events that are on Saturday).
The Countess of Wessex has an engagement on the 18th as well so maybe she will be a no show along with Anne and William.
This information is from the British Monarchy webside Future Engagements page for 18th May, 2019. https://www.royal.uk/futu...5D=18%2F05%2F2019&id=