Board Thread:Questions and Answers/@comment-29625074-20170310215102/@comment-27701762-20170311020328

Yes, you can download the same game from the same Steam account onto multiple computers. If you do that, though, you need to make sure to disable Cloud saving with the game. Otherwise the game will automatically download the progress files for your file onto your sister's computer.

It is also possible with some file copying to have multiple saves on a single computer, but it is otherwise simpler to just use two computers if the option is available.