You can only file one return per account with Turbotax Online,
so you will need to create a second account.
Tip: If
you're preparing multiple returns for family members, it's more economical to
switch to the TurboTax CD/Download software, which lets you e-file up to 5
federal returns at no additional cost. Here is the link to the Desktop
products: https://turbotax.intuit.com/personal-taxes/cd-download/
See this FAQ to create
another account: https://ttlc.intuit.com/replies/3288574