How can I start a return for a different person
Aren't you filling a Joint return? Why? Joint is almost always better than separate.
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-online/00/25596