I suspect that your Mulders are not closely related to Candice's Mulders, although they might be related 2-3 generations before they came to America. Pella was settled by the Dutch around 1847-1850. The next generation went to NW Iowa (Sioux Center, Orange City, etc.), settling there around 30-40 years later. Then a bit later settlers ended up in South Dakota around New Holland, Corsica and Harrison. It is mostly a problem of the land being taken and having to move further west to obtain land for farming. Since both Mulders came from Groningen, they may very well be related.