Sorry Online is only good for 1 return and 1 account. So you need to setup separate accounts for each person. The offer to switch to Online is only good for 1 return and account.
You can start another return in TurboTax Online by:
Logging out if you are in your account
Choose what TurboTax Online product you want to use for the second return
https://turbotax.intuit.com/personal-taxes/compare/online
Create your account screen
Set up a new login for the second return
Start working on the new return
