No, not in Online TurboTax An online account is only good for 1 Federal return per account. If you try to prepare someone else's, it can overwrite your own return. Only desktop editions can prepare multiple returns.
In Online TurboTax the second return would need to be prepared in a separate account (separate User ID). You can use the same email address for notification purposes in the underlying Profile section in up to 5 accounts, but each User ID has to be unique.
FAQ: How do I start another return in Online TurboTax?
https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-onli...
