each taxpayer needs their own a/c but the same e-mail address can be used on up to 5 accounts. using the same a/c for more than 1 taxpayer will wipe out the previous returns.
If you purchase the CD/Download, you can prepare 5 returns using it.
If you are doing it online, each person will need to create an account.
Yes. 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
The Desktop CD/Download program can do unlimited returns.
Thats why if you need to do more than 1 return we recommend you buy the Desktop CD/Download program. It can do unlimited returns and efile 5 for free. And you can buy a lower version. All the Desktop programs have the same forms. You just get more help and guidance in the higher versions. Buy the Desktop program in stores or directly from Turbo Tax here