HI
Raised in the south myself.
Look around you, walk in the forest, drive along a country road. Blackberries prefer full sun!
That doesn't mean they can't produce berries under partial shade if thats what you have. Just position them for maximum solar exposure. Trees steal moisture & nutrients too, depending on the needs of the trees you may have to pamper the berries. Recommend NOT planting within the drip-line of the tree, if possible.
Did you order from Stark? Theirs come with a growers guide.

Cross pollination by raspberries is a puzzle for me. I don't know diddly about it. BUT, the University of Georgia has a Master Gardener program! Students get cut-rate on classes & books IF they volunteer time to the community, something like 40hrs... FREE HELP! lol
Tap the link I've supplies & tap their expertise.

Good luck.
Lex

Here is a link that might be useful: GA Bulldogs