"lets me use the code"  What does that mean?  Do you install the CD on your own computer or use his computer?  Using his computer is ok.  

The Online version is different than the Desktop program and you can't use one to pay for the other.  If you have self employment income you will need to use the Online Self Employed version here,
<a rel="nofollow" target="_blank" href="https://turbotax.intuit.com/personal-taxes/online/">https://turbotax.intuit.com/personal-taxes/onlin...>

If you have the .tax2016 file and want to transfer the info to the 2017 online program you can ... but if you want to use the 2017 download code to pay for the online program that is a hard NO. 

In fact, the family member is violating the rules by letting another person install the program on a computer they do not own.

To transfer from 2016 on your computer into the 2017 Online version,  you need to have the .tax2016 file on your computer. But doing this will clear out all your 2016 entries and you will have to start over.

Select Tax Tools on the side
then click Tools
In the pop up Windows select  Transfer last year's TurboTax return from your computer  link

Here's how to transfer your Desktop version tax return (file ending in .tax) into the  Online version…..
<a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/questions/3006086-can-i-transfer-my-2016-turbotax-return-from-my-computer-to...>

2016 Online to 2017 Downloaded

If you prepared your 2016 return online, in order for your previous year tax information to transfer into your Desktop software you need to download your 2016 Online return as a .tax2016 file.

https://ttlc.intuit.com/questions/1899645-how-do-i-save-my-2015-turbotax-online-return-as-a-tax-data...

If you can't get or didn't save the .tax file to your computer before online was shut down Oct 15 or lost it,  there is a way to do it by starting your return in the 2017 Online version, transfer into that and then you can switch and continue in the desktop version and you won't have to pay for online.  Expand the 3rd section for transferring an Online return in this FAQ
https://ttlc.intuit.com/questions/1901506-transfer-last-year-s-return-into-turbotax-for-windows