Any way you can shade them with an umbrella or some shade cloth for a few days to see if they will recover where they are?
Another thing to do (desperation measure) is to gently dig up one of the most sad looking plants and see if there is a clue to the problem amongst the roots. Disturb the root ball as little as possible, so you can put it back but . . if the potting medium they were originally planted in got too dried out, it may not be absorbing the water you're giving the plants. Poke your finger into the center of the root ball if you can.
Or there may be a fungal growth in the soil that you can't see unless you dig it up.
