Have you asked your brother for help? If he used his own online account then only he can access the account. You cannot access it without the account and user ID he used.
One thing you can do is get a free transcript of the return from the IRS:
You can get a free transcript from the IRS:
https://www.irs.gov/individuals/get-transcript
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**