Each ONLINE account can only prepare one return for one person. Additional returns require separate accounts, and will be charged separate fees, unless you qualify for a simple free tax return.
The DESKTOP program that is installed on your own computer from a CD or downloadable installer can prepare an unlimited number of returns, with the first 5 eligible for e-filing. (The license agreement says you can use it for personal use -- i.e. family -- but you can't charge people to prepare thier taxes using this version.) (Or any version, actually.)
Yes the online version is only good for 1 return per account. So yes you have to pay for each return unless you use the Free Edition. Thats why if you need to do more than one return you should use the Desktop CD/Download program.
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