The photos of the house correspond to Frogmore House which is huge and impressive. But where they lived was Frogmore Cottage which were originally used as servants’ quarters.
As for the * wedding gift * there is no such. They were assigned housing as part of their salary / benefits as officials of an institution as prestigious as the English crown and as they resigned their employment as it is no longer appropriate that they continue to receive benefits and less after the disrespectful way as they did.
Some think that this was a gift from the rich and generous granny and there is no such thing.
The house neither belongs to the queen nor was it given to them.
Here are rules, opinion of the public that maintains them and a whole institutionalized way of proceeding.
If they do not like that they leave but without perks.