Start the game, go to the load screen. Press Ctrl+Shift+I. You'll see something like this:
Adjust the horizontal border of the two, so that you can read comfortably on the right and vertically on the right, so that you'll have something like the image. For this example I'll use Max's saves.
Go to the application tab (1) and type on the search bar save:max (2) or save:kate if you want to delete Kate's saves.
Now, on the left, figure out which saves you want to keep. Note 3 things about them: days played, hour and minutes (3 and 4).
To the right, click on each entry in the middle panel (under the "key" label) and see if the values day, hour and minute (3 and 4) match to the saves you want to keep. If they match, do nothing. If they don't match, right click the entry and press delete.
If you want to delete kate's saves, type save:kate and from the left choose Kate's saves.