Can I use turbo tax free app to do 2 returns?

[mesquitebean]

What do you mean by "free app?"   Are you referring to the Free Edition at Online TurboTax (through a browser), or the TurboTax Mobile App on a mobile device?

If you are using the Mobile App, you can switch back and forth between the App and Online TurboTax on a computer, or Online TurboTax in a browser on  your phone.

Because of that, just as in Online TurboTax, you can only prepare 1 Federal return per account (i.e., per User ID.)

To prepare a second return, the second person would need to use their own User ID for their own account.  If the person doesn't have one, you would need to create the new account before logging in.  And then they would log in under THEIR User ID, not your own.

If you are using the Mobile App, is there a link at the log-in screen for creating a new account and User ID?

Whatever you do, do not log into your own return and prepare a second one by overwriting yours.   That will destroy your return and make it unrecoverable.