You don't need to take the trees down. Growing tree fruits in Maryland takes some effort to manage the multiple common diseases and pests here in our climate.There are things that you can do that should help you to get fruit to eat. To get decent fruit, it takes carefully timed and repeated chemical applications,(several times during bud break and flowering progression) with pesticides and fungicides. It's up to you whether you have the time and interest in doing so.

Do you know what cultivars your trees are? Plums in general are self-sterile, meaning they need another cultivar or ornamental plum that blooms at the same time nearby (and bees) for a good fruit set. Stanley, Damson, Italian, Lombard, and Reine Claude are self-fertile, European-type cultivars. Most Japanese cultivars listed as self-fertile will produce larger crops when planted with a pollinator. Plant two or more European cultivars or two or more Japanese cultivars, but not one of each type. Apricot-plum crosses (pluots, apriums, and plumcots) can be pollenized with suitable Japanese plum cultivars. Perhaps you need to add a tree?

 This time of year it's not terribly uncommon for plums and some other trees to defoliate early. Any damage done by cicadas can be pruned out next year if those branches are not able to flush out with normal sized leaves.

The infection in the 'Tree2' photo is Black Knot. Sanitation is extremely
important in controlling black knot. All the knots on small twigs and branches must be pruned out during the dormant season
and burned. The cuts should be made four inches below the knots. Follow up with the fungicide applications according to spray schedules.

The dropping of fruits could be due to incomplete fertilization, natural thinning (which can be done by hand-they need room to develop), brown rot, or  due to the common pest called plum circulio.

This page will get you started on management. Note that plums are considered 'stone' fruits, having pits like peaches and cherries:

https://extension.umd.edu/resource/watering-fertilizing-harvesting-spray-schedule-peaches-and-cherries

Weeding beneath and clean up (dropped fruit etc.) around fruit trees is important to lessen the pests and disease pathogens present.

Christine