Hi Dina,
Without knowing the names of the plants it's a bit difficult for me to say for certain what is going on. The fact that nothing has been done to the property is probably a good thing. Once people start spraying pesticides they tend to cause an imbalance in the population of good and bad bugs and the need to spray becomes a constant. Of course there is the flip side that non-native pests that don't have predators can become a problem. Some diseases can also get out of hand if the conditions that cause them aren't eliminated.
Your first pic looks like some type of fungal or bacterial problem. Not sure of the species of plant, but Anthracnose or a bacterial leaf spot comes to mind. The different diseases have different symptoms, such as a purple center with a yellow outer ring or starts off yellow and turns black, etc. If you knew the names of the plants I would be better able to search. Do you know the name of this plant? I'm not sure if the first pic is a shrub or a tree but I do see signs of chewing at the outer edge of the leaf at one spot which doesn't worry me too much, but the spots are a bit more of concern. You could try searching at this site by pointing to the type of plant and going from there according to the symptoms.
https://plantdiagnostics.umd.edu/
In your second picture I see a few chewed leaves. Something like this wouldn't disturb me as caterpillars that become moths and butterflies will eat the leaves of plants. There are even leaf cutter bees that cut parts of the leaves from the outer edges and they don't bother me either, even if they do chew up some leaves. I can deal with a few chewed leaves so that there are bees, butterfilies and moths to pollinate my flowers and fruits. I do notice an ant on the leaf, so look for aphids or scale. Ants harvest the honeydo (waste) of aphids and scales and are usually an indicator of another problem and not always THE problem. This site will help you to id some common pests and offers some of the least toxic solutions.
https://woodypest.ifas.ufl.edu/insect.htm
The third pic is a Japanese beetle and they are an imported pest that can be difficult to get rid of. If most of your plants are natives they shouldn't be too much of a problem. The best time to treat for them is in the fall when the grubs are in the soil, but if you have a larger property, that could be prohibitively expensive. Take a look here to see environmentally friendly ways to deal with them and if you need to.
https://www.nysipm.cornell.edu/publications/grubs/
https://www.planetnatural.com/site/xdpy/kb/japanese-beetle-control.html
Unfortunately you aren't at the property much to do some of the inspecting that would be helpful. If you aren't far away from the property, I can give you some sites that have keys to help id trees or you could use them when you are there next year. It's often helpful to id from the twigs when they are in bud as well as the leaves and seeds produced. Trees and shrubs in flower are also easier to id.
Your trees and shrubs should be fine until next year. The one thing you should look into is the Japanese beetle control as that is done in fall.
You can always contact your local extension service for help, but keep in mind that many of the 'master gardeners' that volunteer there just look up stuff on a computer or in a book and will often offer some toxic chemicals. If they can help you id the problem and don't have environmentally friendly solutions, just let us know and we'll find you some.
https://www.clemson.edu/extension/
Another option once you are there full time would be to contact your local native plant society or a garden club to help you id plants. Gardeners love to help with
stuff like that.
South Carolina Native Plant Society
https://www.scnps.org/
Newt
