I looked up the colors at Knit Picks, and just added them to my post so others could see the colors right away. These are the colors, right?
Black Cherry Heather (MC) and Fern (Bumper/Cuff)
Evergreen (MC) and Snickerdoodle (Bumper/Cuff)
I really like the Black Cherry Heather/Fern combo. I think that the Evergreen/Snickerdoodle combo looks nice, too, but I also like how it looks with a darker color for the bumper/cuff...
Like Evergreen (MC) and Coal (Bumper/Cuff)
Or Evergreen (MC) and Mist (Bumper/Cuff)
Another idea, since they are for your mom and stepdad, would be to use Evergreen instead of Fern in the ones for your mom. Then both pairs would have one color in common, without having to match.
I'm sure the clogs will look wonderful!