If a document refers to two men as brothers is it possible that they are not full brothers? Could they be:
What type of “document” makes a difference? Was it an obituary–who gets listed as a “brother” might not be a full biological sibling? Was it an inheritance document? Was it a reference a letter or a story passed down?
From the standpoint of trying to determine parentage and relationships, the difference makes a difference.
Sometimes things might not mean exactly what we think they mean.