Holes in the leaves seldom bother them, Its the sucking pests like squash bugs, cucumber beetles, and squash vine borer that usually take the plant down. I would suspect bacterial wilt on the cucumbers, spread by cucumber beetles. If the older leaves are dying and you still have green growth, Powdery mildew is a possibility as it it affects both squash and cukes. Other cuke problems that sometimes arrives is Anthracnose and angular leaf spot. If it is powdery mildew ( white powdery substance on the affected leaves) you may be able to salvage your plants if they have not lost over half their leaves and you are able to halt its progress with a good fungicide. Baking soda works about as well as anything, Just put a small box of baking soda in a 10 qt sprinkler can and cover all the leaves.