can you use software, such as Turbotax, for more than one person?

Answer 1

Specifically for TurboTax,

According to Turbo Tax, you are allowed by IRS regulation to create and efile up to 5 returns off a single software license. Any more returns need to be filed by paper.

Also, according to them, the End User License allows you to install TT on any computer you own, home or business, allowing you to prepare returns for you and your immediate family.

Each software producer has different rules as to how they want their products to be licensed, so I can't answer that in general.