Just one experience: My son, my daughter and I met with a department chair. She wanted to major in Chair’s department. Son was a sophomore at WC. Before we even got into who Daughter was and why she was here, the Chair turned abruptly to my son.
“How are you doing here at school?” said the Chair.
Son said, “Fine.”
“No really,” pressed the Chair, “how are you doing?”
“I’m doing well,” said Son. “Really.”
“Good,” said the Chair. “How you do will determine in part if your sister gets in.”
I laughed out loud. “No pressure, sweetie!”
Daughter then told the Chair her background and what she was looking for in the department. After that, the Chair proceeded with a full court press to convince her Williams was her perfect place and to apply and let the Chair know if she did. She applied ED and let the department know, sending them special materials, too.
Son had gotten in ED without athletics or legacy. So did daughter, although the above seems to indicate that sibling legacy means something, especially if they feel confident that the older sibling is a solid student and community member. She is a major in that department and extremely happy there.
You be the judge regarding legacies. Admissions has many variables. I agree with Ephman that legacy helps with the tie-breaking factor. It gives a certain amount of confidence to admissions that if one sibling does well, the other is more likely to.
Also, one night at a meet-and-greet for an institution in our city, we met a family with both their son and daughter at Williams, too, one year behind both our kids. We all marveled at the sibling legacy stance in action. Also, my son’s JA has his younger brother there, but their dad was also an alum. So far, with only three families as a data set, sibling legacy exists as some kind of factor.
Good luck!