I'm just curious here. Whenever we walk ours, inevitably someone asks us if they are brother and sister. It doesn't bother me, but I find it a bit amusing. Of course to me they don't look all that much alike, but I live with them! We say Maddie is Jack's aunt, which is not quite true but close enough: Jack's mother's name is Roxy. Roxy and Maddie have the same sire, and Roxy and Maddie's dams are full sisters.
I guess it's funny because my mind does not work that way. I have frequently seen people with two of the same breed (owners of beagles, pugs, and labrador retrievers especially seem to not stray from "their" breed) and I suppose I just never assumed they were related.
Do people ask if yours are brothers/sisters?