All of our kings and the milk had stopped eating sometime last month - but then it's been cold the last several weeks. I personally am not worried about ours (and we have five different types of kings to boot) as I've taken them off of heat completely and tucked them away for the winter. For ours, it's just the timing and with the older snakes, if they've been brumated before, they seem to automatically know when this time of year comes around and stop eating on their own.
The most our biggest male - who's at least 6 yrs old possibly older, and well over 550 grams - has ever lost during the winter months has been between 30-50 grams.
If your snakes are healthy, I'd just let them be and check them once a week to freshen their water and monitor their temps to be sure they don't get too cold and they should be fine. Depending on the ambient air temps in your house (or apartment) you could even turn the heat source off to cool them a touch more.
Jenn