Good Morning,
Brown spots on lilac tree leaves can be caused by several fungal pathogens.  This looks like Lilac Pseudocercospora Leaf Spot.
See attached.

Summer Foliar Lilac Diseases - Iowa State University - At this link: https://hortnews.extension.iastate.edu/2021/08/summer-foliar-lilac-diseases
What's wrong with my lilac? Summer foliar diseases on lilac | Good Growing | Illinois Extension | UIUC

Peach Leaf Curl is a very common issue this year. We had great conditions for it this spring. At this point, we cannot cure already infected leaves. The best way to manage this issue is to spray lime sulphur or copper after the leaves fall around October or before budbreak next March. https://www.canr.msu.edu/news/treat_peach_leaf_curl_now

Looks like you also have shot hole on the peach leaves.
Disease and Insect Control for Homegrown Peaches and Plums | Mississippi State University Extension Service (msstate.edu)

You can send in samples for a small fee to get a firm diagnosis.
Complete details of submitting a sample are at this link: https://www.canr.msu.edu/pestid/submit-sample.

Another option is to have an arborist come out and assess your trees.  Find certified arborists by searching under the “Find an arborist” tab, and using your zip code here—-www.treesaregood.org


I hope this helps.  Thanks for using our service.