That might explain why some of the census records don't seem to know what race the families were. As I said before, though, you need to thoroughly check the census records for the areas you did find the families in. Also, follow the people that you do find, and perhaps in one of the census you will find the ones you're looking for living with them. Then you might get a clue as to some of the names they were using. But you should definitely check out the neighborhood around which Willis W. and Simon B. were found, and look very carefully at the first names and ages.
Good Luck in your research.
Deloris