stewie, to be fair...I think it was the twin thing that through the op, not the sibling thing...
I have 3 boys, my es (who is nearly 13) and my ys (who is almost 5) are a spitting image of eachother, but my ms, who is 7 this year is so differnt to the other 2, bless....es/ys are sturdier build, blonder,blue eyed, rounder faced, etc...my ms is skinny , a bit darker blond haired, very large green eyes,a wider nose (differntly shaped to the otehr 2's) , very small face, but big mouth (in every respect, lol)....heightwise, my ys and ms are similarish, so, we get lots of "are they twins" comments...which now, I cold understand, but when ys was a small Baby and ms was Toddler (21 month between them)....it was simply odd....