Greetings aspirant,

Yes, you can still apply for the first graduate certificate and claim the related benefits , even if your brother already has one but he hasn't used it for any educational or job-related offers. What matters the most is whether your parents have studied beyond school level or not. So if you are the first one in your family to complete college degree and and your brother never used any graduate benefits like fee concession or something, then you're eligible for using the certificate for yourself. Just make sure to clearly mention in the application that your sibling has not availed any benefits using the certificate.

Thank you