I can't recall if I posted this before, but I like to think that the different Soongs - Arik, Noonian, & Alton - were actually clones of Adam Soong, created by himself. That would explain why they all looked the same. I know we (the viewer) are supposed to just suspend our disbelief that they all look the same, but I think my theory kind of makes sense even within the established Trek cannon. Their different personalities could be explained by things like each clone growing up in different environments (a la Shinzon vs Picard in ST: Nemesis, or like the film The Boys From Brazil), or possible self-genetic tinkering (Arik Soong was altering humans genetically).
Unless I missed something or don't recall, we've seen multiple members of the Soong lineage, but never any women - no wives to become mothers to any of the Soongs. Cloning would explain this.