I only have one boy of unknown parentage as he is an adoption but my guess is that they probably do "know" family by scent if not sight. Their differing reactions to "family" probably relates back to the "pack" mentality. A female may have two daughters that she treats completely differently due to her perception of their ability to challenge her as "alpha" female in the future. I would guess it is similar for males. Time together as a "family", as with humans, is probably also a factor. Just my thoughts.
