Princeton Questions in the Common App

Answered

This area within the family section is intended for gathering some data points about your siblings. It is not an essay prompt whatsoever otherwise it would say, please write an essay about your siblings.

"You have the opportunity to add information about your sibling(s) to what you provided in the ‘Family’ section of the Common Application. Please list their name(s) again as well as highest education level achieved, and, if applicable, the college or university they attended, dates enrolled and degree received (BA, BS, MD, etc.)."

I don't know what they do with the data but maybe it helps the admissions/financial aid office corroborate what is being submitted on your FAFSA and CSS Profile. If you are applying for financial aid, perhaps they want to know who is going to school, how much longer they are going to be in school, and they can figure out how much that school costs and determine your financial aid award with more accuracy. Since siblings do not count as legacy, I don't think this sibling information will influence the admissions decision. However, if you have a couple of super smart siblings ahead of you and they all went to Ivys and Elites and getting advanced degrees etc., it takes some of the risk factors out of your decision.