Perfect. Once you're in Steam, right click on Our Life, and go to "Manage", and then "Browse local files". That will open up the game's directory. In there you'll see a folder called "game". Click in there, and look for the .rpa files (they'll be called dlc_step_1.rpa", for example). Take all of those RPA files out, and put them in the "game" folder of the Mac version. That is a bit trickier to find, as it's very deep, so here is the file path:
OurLife.app > Contents > Resources > autorun > game
Hope that helps, and thank you for playing!