You might have Early Blight. Cool weather plus wet plants can lead to blight. Plants of the nightshade family are especially susceptible to blight. That includes peppers, tomatoes, potatoes and eggplants.
If it is blight you should destroy the sick ones. Treat the the rest with copper solution. Make sure they are not crowded together. Try not to touch the plants if you do wear disposable gloves.
Avoid watering from the top, wet leaves lead to disease. Always bottom water your plants.
Good luck
