Those Boarders Might not be Boarders

Is there one or two "boarders" with your family in the census? Just because they are listed as a "boarder" doesn't mean that they aren't related. Boarders could easily be nephews, nieces, or other family members temporarily staying in the household. They may be a clue. Try and find them ten years earlier or ten years later and keep the names in case they appear in other documents.