Q.peach trees dying
What would make the leaves start falling off of a peach tree that has peaches on it? The peaches are still growing but the leaves are dying out.
Some leaves will yellow and drop off the tree normally, as they age.
If the issue is more severe, you will need to investigate a bit further.
Are there any marks, spots, color changes on the leaves?
Any cracks, markings, soft spots on the branches or trunk?
Any signs of insects?
Here is a link that has information on the most common diseases of Peach Trees.