Allowing family member to use my Desktop TurboTax Deluxe

Yes. You can e-file 5 tax returns using the same TurboTax Desktop software. The Product Key is only used once when TurboTax is initially installed on a computer. If another person wants to use it on another computer, they will need to sign in to the owner's account and download it to their computer (or the owner will need to sign in to their account on your computer).

I purchased the turbotax deluxe disc.  I have only used it to prepare 2 taxes.  How can my niece use the disc on her computer to prepare her taxes?

The TurboTax user license allows one user to install copies of TurboTax on up to five computers that the user owns. You can also prepare multiple returns, including returns for other people. But the license does not allow, and has never allowed, one copy to be shared among different people.  This year, that license is being enforced by requiring users to log into their TurboTax online account when they install the program for the first time. This locks one particular copy of the program and one license code to one user account. The only way you could install the program on a computer that you do not own, would be to give the other person your online username and password. And even though that workaround might allow the installation, it’s still a violation of the license.  

"If another person wants to use it on another computer, they will need to sign in to the owner's account and download it to their computer" 

If I do that another person can see, my tax return information? because I login my account on their computer for them to download and file their return. 

Yes.  They will have full access to your account if you give them your login information.

@Phyo A 

@Phyo A   NO they can't see your tax returns.    Not unless they were done on the same computer. The returns are not saved or stored in your online account. Only the License Code. A desktop return is only on the computer that prepared it.