After looking at all your pics it does seem like your sick plant has some type of mildew/mold or wilt much like I have seen sometimes on tomato plants. The easiest treatment for that and will not effect your plants is to dilute some skim milk with water in a spray bottle and spray the effected foliage. 2 to 3 Tablespoons of milk per quart of water. This kills mildew and fusarium wilt on tomato plants but you have to get underneath the leaves also....big job for those big plants and spray it every other day or so. Good luck.