Actually I don't like to add calcium until they are actually laying. Some do, but I don't want to overload their kidneys.
I would guess that their point of lay time arrived with the cold weather, delaying them until spring. Marans aren't a breed known to really pump out the eggs like a Leghorn would, so it's not surprising to me that they are running a little late. Don't feel too bad; some breeds take longer, and now and then hens don't lay til nearly a year, or even over a year. I imagine as soon as it starts warming a bit, you'll see those combs brighten up and they'll start squatting for you.
You could certainly try the protein and even a little extended daylight if you want, though I'm not sure it would be worth it to go out and buy a light socket and timer this late, as the days are lengthening a fair amount already. If your layer is 14%, IMO, that's a bit skimpy anyway.