Dude! That's gotta be spider mites. You need some sort of magnification to really get a good look at them.
Are all three plants the same strain? Some are more resistant than others. I recently had mites and was growing three different strains in a very confined space, but only two of them were really affected by them, one strain showed almost no affect (effect - affect? Shit I can never remember which is correct)
Try using some Azamax. There are other solutions, but I have used this one personally and it does work. Treat every two to three days for about a week to ten days. Sterilize everything in the area with a 50/50 water & rubbing alcohol solution. Try not wearing the same clothes you wear outside when your in your garden area. Clothes, pets, ventilation are primary sources for mites, if they weren't already there if/when you received plants from someone.