AT first glance I was looking for the typical apple issues like cedar apple rust, spongy moth defoliation and other similar issues for apple trees.  Your photos did not seem to indicate any of those issues.
Our plant pathologist, saw your post and offered the following advise:
"We have seen a lot of early defoliation in crabs and apples over the past few years.  It is typically a combination of early fungal disease/insect issues that stress the tree, followed by drought conditions, which further stresses the trees.  I have seen this in my own wild apples but they always seem to bud out just fine in the spring.  To control the fungal disease issues, you would need to spray fungicides weekly from green tip to about the end of June.  Most home gardeners do not want to do this, so they just live with some of the damage.  It probably will not kill the tree, but over time it can cause some stress.  I would be sure your trees are pruned well to open them up to air and light so leaves dry quicker and are less prone to diseases.  Fertilize the trees in spring if they are young.  Mulch the trees to preserve moisture or irrigate during periods of drought to remove further stress."