Are they behaving differently in any other way besides their lack of appetite? Are they lethargic/not playing or moving around as much as they normally do, are they sleeping more than usual, are they hanging out on the bottom of the cage at all instead of perching normally, are they constantly "fluffed-up"? Any vomiting? How do their droppings look, are they at all watery, loose, runny, or do they have any bubbles in them?
Whenever a bird stops eating a certain kind of food, like the "Chop" in this case, but they are still eating their pellets/seed-mix normally, then it's typically that they have become bored with that particular Chop or veggie, fruit, etc. So in that case usually just changing the Chop recipe or the type of veggie or fruit will get them interested again and that's it...However, if they stop eating everything, their pellets/seed-mix along with their veggies, fruit, etc., that's when you have to be concerned that something else might be going on. You want to watch their overall behavior very closely for as long as they are refusing to eat to make sure that you're not seeing any changes in their other normal behaviors, or to make sure that their droppings are normal, because a lack of appetite combined with other abnormal behaviors/signs & symptoms is an indication that something medical/health-wise might be going on. Weighing them ever single day on a digital kitchen scale is a great idea, because they should not be losing weight, they should be maintaining their weights. Be sure to weigh both of them at the same time each day, first thing in the morning before they eat their breakfast is a good time because you'll get an accurate weight without any added grams from food they ingest. It's a good idea to get a little notebook and make a weight chart for each bird, and have each daily entry include the date, the time, and then the weight; the reason you want to do this is just in-case they are actually ill and you have to take them to your CAV, you can take the notebook with you for the Vet to see how their weight has been tracking since you first noticed that something might be wrong...
It could be the weather if the room they are in is effected by it, but if it's weather-related it should be short-term. I'd weigh them every day, watch them both closely to see if any other behaviors are off, try changing-up their Chop recipes to see if that entices them to eat, and if they still aren't eating their pellets in the quantities that they normally do each day in the next few days, or if you see anything else that's off, then they should get to your CAV for a wellness-exam and at least a Fecal culture on both of them to check for either a GI infection of some type, or even a parasite.
The only good thing about them BOTH acting the same way is that if they are sick, that means it's probably something simple and easily treatable like a bacterial or fungal infection, or a parasite in their GI tract, etc. because it's something that was/is contagious to both of them...
Nothing.
