Can I use my email address to create a second Turbotax account to do my late father's taxes? How do I do that?

Yes you can use the same email address for 5 accounts.  You can start another return in TurboTax Online by:

1. Logging out if you are in your account
2. Choose what TurboTax Online product you want to use for the second return
3. Create your account screen
4. Set up a new login for the second return
5. Start working on the new return

I am not getting to the choose the product after logging out of my return account.  What am I doing incorrectly?

Have you created the new account yet?   If you are signed into your TurboTax account, you should use the Sign Out function - from the left side menu, at the bottom of the screen.    Then on the sign-in page, select Create New Account.  You can use the same email address, you just need a new user id/password combo for your dad's return.  @mland 

If you are unsure if you created the new account yet or not, you can find all the accounts created with your email by going through the steps in this article >>  How many TurboTax Accounts do I have? 

When I enter my email address in for the new account it says the address is already taken.  So what do I use for the Email address if I can have up to 5 returns under the same email?

Can you clarify if you are using TurboTax Desktop or Online?  If using Desktop you can login with the same credentials you have been using and just create a new return using the steps above.   If you are using TurboTax Online you will create a separate account using a separate email. 

@mland 

so basically the online version of Turbotax does not allow 5 returns to be filed under one email.

That's correct, you can only create one return per account in TurboTax Online.