is it cheaper to purchase the software at a store for a family of 4 basic returns instead of online purchase?

You can check the retail stores, as sometimes they do offer sale prices, and as they have products in bulk, different retailers offer different prices. If you wish to purchase from Intuit directly, here is the link to purchase: TurboTax Desktop

Thank you for choosing TurboTax.

I bought the Deluxe online edition 8 returns, but how does this work? My parents used 2 and how do I use it? When I try to put the code it doesn't work. Where should I put the code when it has been already activated?

You will need to first sign in to the Online account that was used to activate the license code- Then you will be able to enter the license code on a different computer and you won't see anyone else's return as their files will be on their computer.

Thank you for choosing TurboTax.