Thank you for this second image. Your squash could have Verticillium wilt a fungus  infection or another leaf wilt of the viral type passed on by white fly.  One other possibility is a lack of nutrients such as potassium that causes leaf curl like this. While I cannot be sure what is causing the leaf damage I can offer the standard advice to fertilize with a complete plant food that contains potassium (Osmocote does) and if the plants continue to go downhill you will need to dig them out and send them away with the garbage.  Preventing these diseases is helped by keeping weeds away which can harbor white fly, having good drainage and good air circulation around the plants and not putting  young plants outdoors too early. Heat loving tomatoes and squash can be weakened if placed outdoors while the nights are still cool and below 55 degrees. A soil that is moist but not wet also helps. You will always learn a lot when a plant fails so don't give up. Keep growing, Marianne Binetti