Hi,
You can do up to 20 returns in one TurboTax Online account. However, if you want your friends to have access to their returns without seeing other people's information, then it would be a good idea to have separate accounts for each.
With TurboTax Online, you pay per return, based on what is on the return, and you can see the prices on our website here: https://turbotax.intuit.ca/tax/pricing
Retailers like Walmart, Costco, Staples, etc... sell multi-return packages. You can download the software onto your computer from this link, install it. Here's a link explaining all the steps involved in installing the Desktop version.