A few questions about growing peaches in Georgia

I live in NE georgia, my yard is in a broad, gentle swale meaning that 3 sides drain into it and there is a 40' tall Leyland Cypruss hedge on the fourth side, so air movement is limited. I have lost every peach crop for years due to brown rot. I do not want to repeatedly spray fungicide on a tree in order to chemically stop the rot, for a variety of reasons. Even this year, when we are having a severe drought, I will lost most of the fruit.
I had some volunteer peaches germinate in a flower bed a few years ago apparently from some composted storebought peaches. I potted them up on a whim, and once they were large enough to bloom, I planted them last year. This year, even though the plants are only 8' tall with a 1" stem, one of the plants has dozens of fruit which, although a bit smaller, have good flavor and there is very little brown rot of the tree. I am considering saving the seed from this tree and attempting to start more trees.
My first question is, should I cut the grafted, brown rot affected tree to the ground and let it stump sprout in hopes that the root stock is more resistant? Can grafting from the brown rot resistant tree be done to a tree with the brown rot disease? The tree is a dozen years old and about 4" in diameter.
A second question is with the volunteers, if they are bearing when they are only 8' tall, does that mean they are dwarf trees, or is this normal peach behavior and they might be full size trees in the making?
Third question, has anyone who lives in this climate had success with any varieties without spraying that has to contend with reduced air circulation like my yard?