Everything that I could share about growing cherries here in the south would just be from reports others have made. I originally wasn’t going to try growing any cherries, but after reading that there were bush cherries that could actually produce good fruit here I did end up planting one. There is much posted on the forum about what might work well in Alabama, my neighbor to the west. This is one of the many threads that I would direct you towards:
As a result of the difficulties I would have in producing sweet cherries I am fine with growing sour cherries instead.
Not knowing anything about the soil where your grandparents are, you might want to read up here on the forum about whether it is actually beneficial to turn the soil in the orchard into what we generally think that great garden soil should look like. I know that I certainly scaled back my plans after reading what people’s reports were when growing fruit trees in soil that was rich. Alan here manages many private fruit tree orchards and has many years of experience.
The subject of installing irrigation is another one that you might wish to consider leaving off, especially when working with well-meaning grandparents.