can i file taxes for someone else

Online is only good for 1 return per account.  But you can use the same email address for 5 accounts.  You can start another return in TurboTax Online by:

1. Logging out if you are in your account
2. Choose what TurboTax Online product you want to use for the second return
3. Create your account screen
4. Set up a new login for the second return
5. Start working on the new return

You can have up to 5 accounts can be tied to the same email address.

The TurboTax online editions are only for completing one tax return per account and User ID.  To start another tax return with the online editions you will need to create a new account with a new User ID.