This rarely ever happens, especially with beginners but it sounds to me like they're not getting enough water. I'll explain why:
First, you have a fan blowing at high speed over the cups. This will dry out the soil - even in larger pots - quite quickly. Second, you are only spraying water into the cups which I assume means, not that much water. If you combine those two things the roots would hardly have enough time to process adequate water to maintain a healthy plant before the soil dries out.
If I have the 'facts' wrong above, you can straighten me out, but I would fill some larger pots (not too big - 6 inch maybe) with pre-moistened soil that contains a very small amount of nutrients. (If the soil you are using already contains nutrients that isn't necessary. Having a
few extra nutrients won't hurt as the plants are already damaged and will use them to recover. Very few though - too many will finish them off. Again, if the soil already has nutes, don't worry about it.) Remove the plants - soil and all of course - from the cups when they are dry as it is much easier to get them out in one piece ... the whole thing should almost fall out of the cup when dry. Transplant into the pre-moistened soil in the larger pots. If the soil is wet enough it will soak into the transplanted soil ... if not you'll need to add a little more water to the center. Regardless of how it happens, make sure the new soil/pots are soaked with water. Not dripping wet, but very moist. Now leave them until they dry out before watering again. Once they dry out, water until it comes out the drain holes in the bottom, then wait for it to dry out again and so on. (In my opinion you can throw the moisture meter away as long as you water like that but I know lots of people like them - many of the same people that have watering problems.
) I'll probably get killed for that. LOL
Look at if logically: If the plants have everything they need (and not too much of it) they will grow just fine. If not, problems occur. Look at your setup in that regard and it really helps to sort things out on a basic scale.