dying ornamental cherry trees
We need more information to be able to diagnose the cherry tree problems. Please attach photos in a reply which includes photos both close up of dying (not dead) leaves and wide angle shots showing the trunk base and whole tree in its site.
Also give us more information about the tree's location (sun, moisture, etc.) Any changes in the vicinity, such as construction?
Both cherry trees get sun mid-day but there are a lot of other tall trees around so they do not get direct sunlight all day. Our ground is a lot of clay covered by ~ 6 inches of loom / soil. When it rains the soils drains slowly. No changes to their surroundings. The taller tree has a split in the trunk which has oozed sap but appears to be healing. House is ~ 37 years old, but we have lived here for 5 years, so I imagine these trees where planted with the original landscaping.
The tree in your first photo has severe trunk damage. The tissue that transports water and nutrients in a tree is located right underneath the bark. When this tissue layer is damaged, water/nutrient transport is going to be impaired which will result in dieback in the tree canopy. Also, we can see the tree gets a lot of shade (moss is growing on it), so it may not have the amount of sunlight it needs to really thrive. Many cherry trees also get a leaf spot disease (cherry shot hole: https://extension.umd.edu/hgic/topics/cherry-shot-hole-flowering-cherries) which can lead to early defoliation in late summer. The trees might also be having some trouble in poorly drained soil, which can lead to root decline (which also results in dieback).
If the tree with severe trunk damage is so close to your home that it may be a hazard to people/property, consider taking it down and replacing it with something better suited to shady conditions. If you wish, you can get the opinion of a certified arborist. You can find one near you using the following page. http://www.treesaregood.org/ An arborist can evaluate trees for structural problems and prune or take down the trees safely. Cherry trees can go for awhile not quite looking great but they can still be useful for supporting wildlife if that is something meaningful for you. Trees that are located in an area where they pose no hazard can be left to decline naturally as wildlife snags.