Two of my sons are at the same college, a year apart, and people occasionally confuse them. You wouldn't think that was odd, two brothers so close in age to eachother, except for the fact they are really different. One is skinny, one is muscly. One is fair-haired, one has very dark hair. One has bright blue eyes. The other dark hazel eyes. Their noses aren't the same. The face shapes not the same. They are the same height but with different body types. I know I'm their mum so they won't look the same to me, but they have totally different builds and colouring. One of them looks like their dad. The other looks like me. And they are on totally different courses - one doing the Arts, one doing Sport coaching. I don't get how people confuse them.
And they don't hang round together at college, and their groups of friends barely overlap. So it's not like they're always together. Son 4 said to me the other day that a girl he knows saw Son 5 at a breaktime, and asked straight away if that was his brother. Yet they look nothing alike and don't even have the same facial expressions. Maybe it's just other people see something we don't.