If you bought the Desktop CD/Download program they can use it. The Desktop program can do unlimited returns and efile 5 for free. Go up to File-New Tax Return
But if you used the Online web version, 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-onli...
Or go to the IRS Free File programs
Free File: Do your Federal Taxes for Free | Internal Revenue Service
