Crab apples may be suffering from apple scab which is a fungal disease and facilitated by wet weather. It causes leaves to turn pale and drop. Depending on where the trees are growing the soil may be too wet and the trees are wilting because of too much water. Too much water causes root rot and because the roots are bad the tree wilts.
Too much rain and pollination doesn’t happen and that will affect how much fruit is produced. I wish I had more than speculation to offer.

Thank you for your response.  I hope the disease is not terminal.

It is rarely more than a nuisance.
https://extension.umn.edu/plant-diseases/apple-scab#:~:text=Apple%20scab%20is%20the%20most,olive%2Dgreen%20to%20brown%20spots.