How many family members you can file for under one account?

The TurboTax Online editions are only good for one tax return per account and user ID. You can create 5 accounts with the same email address, but you will pay for each program separately. See this FAQ:https://ttlc.intuit.com/questions/1894512

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.