We don't see any particular disease or insect. Keep in mind that at least half of plant problems are environmental/site issues. And when disease and insect do arrive, they often come as a result of underlying cultural/environmental problems that made the plant weak already.
These trees could have browning for several reasons, but especially drought damage (last summer many areas in Maryland had severe drought.) In addition, these three trees are close together and their roots are competing for moisture (and nutrients.)
They do like a moist soil, but not sodden all the time. So, if, the year before last when we had abnormally high rainfall, they were sitting in water, that would also damage them.
That said, they have a lot of green life left. We'd recommend that you can let the dead material fall off naturally and be sure to water during any dry spells this year--spring through fall. (Fall is the worst time for drought.) Put a hose on a low stream and move it around under the canopy or use soaker hoses.