You can install Turbo Tax on 5 computers YOU OWN. You would have to give them your online account info to activate the program. But they will not see your info and returns. The returns are only kept on the computer they were done on. They are not stored or saved on Turbo Tax online. They can still use their account to efile their own returns.
See this FAQ for why do I need to sign in to an Intuit Account this year? And how to Install and Activate
https://ttlc.intuit.com/turbotax-support/en-us/help-article/license-information/install-turbotax-cd-...
Post on installing on family and friend's computer. See 2 employee answers,
https://ttlc.intuit.com/community/taxes/discussion/re-if-two-or-more-families-file-under-one-turbota...
