I look at early days baby pictures of Luke and I see Sammy.
I look at early days baby pics of Thomas and I see Sammy.
So…

Thomas is my sister Rachel’s doppelgänger.
Luke is mine.

Thomas and Rachel at 9 months is the same child.
Me and Luke at 9 months? Same child.

Me and Rachel, obviously related, but not doppelgängers.
Thomas and Luke, obviously related but not  doppelgängers.

I look at early days baby pictures of Luke and I see Sammy.
I look at early days baby pics of Thomas and I see Sammy.
So…