I am not sure what is wrong not enough info. When I grow peppers in pots, I use the self watering kind, as well as a ceramic gizmo that holds a soda bottle of water that I can add water soluble fertilizer to according the package directions.
I also use a soiless mix so that my tendancy to overwater doesn’t lead to root rot.
Have you tested the ph, and nutrients? Are you watering too much or too little? Are you watering overhead? Have you taken a magnifying glass to look closely at them and the under side of the leaves?
Have you checked the roots of one of the plants to see if there is anything amiss?
I wanted to re-pot, but not wanting to gamble with peppers already growing, wasn’t sure if it would be their demise. I rarely have to deal with plant diseases or problems, so I dont have stuff the check nutrient levels. Normally, we just move on after a plant fails and replace it with something else, but I want some really hot peppers. Under normal condition, it is either too much or too little sun that is our problem. We water everything at the ground, never above on the leaves.