You know what I find even weirder than the names? The fact Constantijn and Laurentien have known each other for their lifetimes, played with each other as kids. How can you fall in love with someone as an adult if you have been hanging out with that person all your life and treated them as if they were, say, first cousins? How can you fall for the kids of your parents' friends anyway?! There's something so, well, obedient in that, so submissive, so meek. There's also something slightly creepy in that concept, I think.
That said, I don't know their entire story, so there may be an explanation for this. Also, Laurentien is my second favorite Oranje royal (first one's name starts with a B, of course!)