This article could have been written by me, except that I am the Mark in the story and the age difference between me and the youngest, the sister Padmini is six years.
I have read the book The Sibling Effect by Jeffrey Kluger in which he points out ““Siblings are the only relatives, and perhaps the only people you’ll ever know, who are with you through the entire arc of your life.”
The four of us have been separated by distance sometimes substantial, sometimes not but the bonds have been very strong and continue to be.
What is heartening is also that the next two generations of cousins seem to find the relationships very comfortable also.
I am all for a Siblings Day. Unless it already exists.