Dutch Royal Coat-of-Arms, Standards and Flags

[Marengo]

I came across these two coat-of-arms, they look the same on the first glance but I notice that in the first picture the middle shield is in the form of a shield while on the second image it is in the form of a circle. I wonder why this difference has been made, maybe the circle-thing is for members who marry into the RF? I remember that Laurentien has a round coat-of-arms too. This one is of Máxima btw, the castle with the cypresses is the coat-of-arms of the Zorreguieta family. I suppose the first one is the c-o-a of her daughters. The horns represent Orange I believe and the lions represent Nassau.