I expect Leonor will use de Borbon y (husband's familyname) for her children and in that order the Borbons would remain on the throne.
I should hope not! The only reason Leonor is a Bourbon is because her father is one, his father is one, his father was one, etc, etc, etc. The House of Bourbon is flourishing and what unites them is their common agnatic genealogical heritage. Creating a new house of the same name is unnecessary.
I don’t believe that the children of Victoria and Daniel legally have a surname. Victoria doesn’t have one. A surname and house name are not the same thing.
No surname, but Sverre Magnus is a member of the houses of Glücksburg and of Oldenburg so he could adapt either of those as a surname and still maintain a nod to his dynastic heritage.
1