Answer: You are right, both cultivars are disease-resistant--good choices! All apple trees go through what is termed "June drop", where they drop excess fruit. Since your trees are so young, I wouldn't worry about the fruit dropping off--the plants still need to get established and forming fruit takes energy away from the developing roots and branches.
Both these varieites are resistant to apple scab--one of the most common apple diseases. It could be that you have some minor scab damage (the plants are resistant, not immune); if just the occasional leaf has spots, I wouldn't worry. There are a few other diseases, such as cedar-apple rust, that can also cause leaf spotting. Again, if it's just a few here and there, I wouldn't worry.
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