We have two different locations to review Sibling Attending information: Reports > Sibling Applications and Admissions > Validate Priorities.
The Sibling Applications reports lists every application and their listed sibling that attends/has graduated your school. In this example, student A has two sibling attending your school, sibling B and sibling C. Student A still only have one application.
The Validate Priorities page lists the priorities that need to be validated before entering the lottery. Student A still only has one application, with this page again listing the multiple siblings at the school. A school admin would then approve or deny this priority before the lottery.