Definitely have spider mites. I personally like using isopropyl as the control, but in this case I advise getting something like
Azamax and treating the plants, the pots *and* the tents with it. Then you're going to have to pay closer attention to who and what gets in with the plants, as well as whether or not you're wearing clothing that's been worn outside, etc. Any and every thing can and does act as a carrier for the mites.
Next, they don't look all that bad, but they look cold to me. The clawing can be caused by nitrogen toxicity, but it can also be caused by too hot or cold conditions. Too cold will also cause what appears to be a bit of a phosphorous deficiency to my eyes.
But, right now we're kind of guessing. We don't really know what media these are planted in, what the environmental parameters are, what the husbandry consists of, pH of feed, water and media, lighting (light spectrum has an effect on nutrient utilization and uptake), etc.
What I would do FIRST is take each plant and clean it up. Get out everything that looks "hairy", the leaves too closely grown together on the inside that prevent good air flow and, this is key, the ability to make observations. This is the beginning of your canopy control.
After it's cleaned up, get it treated for spider mites. Use the label directions for chili peppers and/or tomatoes, that kind of annual consumable. I want you to use either
Azamax or Azatrol specifically because they are known not to cause resistance in mites. Resistance is very real and a very big problem. These products are also safe for consumables and have a good established history in farming circles.
When you're done cleaning them up and treating them, it's time to get clothing and shoes into the washer and/or freezer. You need to not continually reinfect your grow space upon entering.
After that, get a handle on the environment and report that back to us. If the temps are cool, then the next thing that needs to be done is warm the plants up. If temps and RH are in good ranges, then we can address specific nutritional issues.
So the information we're going to need from you is the following:
Media (soil, peat, coco coir, soilless potting mix?)
pH parameters for feeding and watering
pH parameters of the media (slurry test is best for this IMO)
Feeding strength, I prefer EC but others use ppm or TDS (both derivations from EC)(if organic, this doesn't apply)
Temperatures day and night
Relative humidity levels day and night
Lighting
Plants age and type (clone or seed starts)
