How do I use my Turbo Tax Login account to do someone else's tax return?

[JulieS]

You don't. In TurboTax online each return must be done in a unique account. You will need to create a new account for the second return. 

In TurboTax Desktop (from a disc or download), you can create multiple tax returns. 

[ellee113]

I always purchase the download edition which lets you e-file 5 tax returns for free (and 1 state -additional states cost $45) and ends up being cheaper than the online option.  I inevitably end up 'helping' one of my 20-something kids or other relatives file their taxes (this year 2 kids and my partner's aunt).    It is impossible to find the download edition on the TurboTax website - you need to specifically search for it.  Google 'Turbo tax CD/download'  I realize this does not answer your question - but is how I solve for the problem.