Australia News on July 14, 2021

The citizenships via conferral form have a section where it asks for the details of siblings of the applicant including date of birth, place of birth, and full name. I have four siblings, and all of them live outside of Australia. I have not talked to them for years because of some family issues and don't know their date of birth. It will be very awkward if I talk to them now and ask their date of birth. What options do I have, and why does the citizenship application asks for these questions? I mean do i really need to be accurate or i can simply guess.