both of these are being sold on Costco and I don't understand what the difference is. Is the Online edition the same as the "online software" on turbo taxes website? As you just buying a code to use through the web interface?
Yes, the Online Edition is the same as the Online version that we have on our website. Both the Online versions and the CD/Download version can create the same types of returns, however there are some differences. This FAQ has more info: https://turbotax.community.intuit.ca/questions/1658842
If I buy the online version bundle form Costco, can I spread the number of returns to different accounts? Or do they have to be all done under 1 account?
The desktop version seems to allow you to install it on 3 computers (but you have to uninstall it first before you can install it on another computer???)