It's highly likely a common leaf spot disease known as apple scab is the culprit afflicting your trees. You can try to curb the effects of the disease with good sanitation and pruning practices, but often times the disease will still need a preventative fungicide treatment. And if you wait until you see symptoms of the disease, then it's likely too late, and any fungicide will not be of any effect. The good thing is, is that it won't kill your trees, just ruin your crop, and be a highly unsightly tree toward the end of the season.

Using fungicides for apple scab, the soft developing leaf tissue is the most vulnerable and needs to be protected. So your first application should be after bud break when the leaves are in a 'mouse ear' condition, meaning just really small developing leaves. Fungicide applications should continue until the leaves harden off, till about just after flower petals fall. If you are trying to do organic (sulfur,copper) then you'll likely need to spray weekly, 7-8 applications total. Otherwise, contact fungicides like chlorothalonil, mancozeb, or a systemic like myclobutanil you could probably get away with monthly, 2-3 applications total.

And know that fungicides are not good for pollinators, organic or not. So it's a good thing to try to avoid spraying the trees while they're in full bloom, and if you must, do so during evening hours. Otherwise try to time your applications just before it flowers, and just after the petals fall. And the one application, after the petals fall, should be the last one you need. Also: if you do choose to go with a fungicide, please do thoroughly read the label for specific directions, rates and efficacy; as it's not only for your safety but the benefit of the environment and ecosystem.

Here is more information on apple scab: https://extension.umn.edu/plant-diseases/apple-scab

Best of luck.