Research of 1894 Michigan Census turned up one and possably two more brothers.
Edward and his family along with a "border" named Robert Kops.
Muskegon County Clerks office has Edward as the son of Carl. His obituary puts him in the same geographical area as the rest of the family until he later moved to Ravenna with wife and children, where he died. His wife was Emily Schultz.
So far, the 1894 census is the only mention I have found of Robert. Robert was within a few years in age as the rest of the brothers. I suppose that he could also be a cousin.