If you look at other pictures, it's easy to see they don't look any more alike than any two relatives, even at the ages they are in this photo. In this photo I

If you look at other pictures, it's easy to see they don't look any more alike than any two relatives, even at the ages they are in this photo. In this photo I think several effects combine to convince people they share similar looks. The first is the power of suggestion: We've been told they look alike. The second is the same beard style covering half their faces. The third is that the light is soft and washes out their features, leading to any of their features seeming not too dissimilar even if they aren't the same. Since this happens for basically all of their features, the effect can make it seem like they look alike and to the extent it doesn't, see the power of suggestion above.