If Cristina and the children were in fact absent, and if the reason was because Inaki wasn't invited, Juan Carlos should be ashamed of himself, IMO. Juan Carlos has happily rubbed shoulders with people who make Inaki look like a choir boy so I doubt it would have killed him to be civil to his son in law for a couple of hours for the sake of his daughter and especially his grandchildren. If the issue was Inaki being in an official residence I'm sure any number of extended family or friends would have gladly opened their homes for the celebration. If anyone here is showing an excess of pride and holding a grudge it's not Cristina, it's her father.
Juan Carlos has been petty throughout this process, though. I recall, for example, an article in Vanity Fair in which he authorized one of his closest friends to speak disparagingly of Inaki. Contrast that to another article in the same magazine in which Cristina's closest family and friends spoke and one of the upfront conditions was that they didn't discuss either Inaki or the Spanish royal house.
I'm not sure why they chose such a provocative picture to publish. They could have taken a nice one of Juan Carlos, Felipe and Leonor. Or, if Cristina and the children were in fact there, they could have done one with JC and all the grandchildren. Or they could have done no public picture at all as it was well emphasized in the Spanish press that this was a strictly private event. Instead they choose a picture of the entire family, except of course one of his daughters and, oh yeah, half of his grandchildren. They must have known the absence would be part of all the headlines and provide the opportunity for still more discussion about the seemingly endless toxic relationships within the family. More importantly than all that, it seems needlessly cruel towards the Urdangarin children.