I imagine there's a picture very similar to this with filly Twilight, teen Cadance and teen Shining Armor somewhere in a (in-universe) photo album. (Twilight would be holding a book instead of the hat, but you get the idea. )
I never really thought about this but Big Mac, Applejack and Apple Bloom remind me of my mom and her sister and brother growing up. They had a younger brother but he came along later.
Big Mac reminds me of my Uncle Danny. He was the first to be born. Plus later on in life, he would go on to own horses. Applejack reminds me of my Aunt Linda. She was the second to be born and Apple Bloom reminds me of my mom. She was the third to be born.
My mom and my aunt and uncle don't have anything in common with Big Mac, Applejack and Apple Bloom. This just reminds me of some pictures I came across of my mom and her sister and brother. They were together. That's the point I'm trying to make.