Can I file my brothers taxes on my app

[VolvoGirl]

Online is only good for 1 return per account.  But you can use the same email address for 5 accounts.   How to start another return in the Online version

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-onli...

[DoninGA]

No.  You will have to create a new account with a new User ID to start another tax return using the TurboTax online editions - https://turbotax.intuit.com/personal-taxes/online/

The TurboTax online editions can only be used for one tax return per account and User ID.  You can have up to 5 User ID's associated with one email address.