Congratulations, those are very valuable trees. As Thelka mentioned the meats of the black walnut are not the same as the English walnut, which is quite large. The nuts are usually cracked with a hammer around here, all parts of the tree will stain your skin and clothes. If you want to use the black walnut medicinally, it is the inner bark (just before the cambium layer) that is used in tinctures and as a tea. Please do the reading before you use the medicine, I have heard it can be tricky to get it right.
As for care of the trees, prune out all dead wood just above the branch collar. Do the same to all crossing branches, don't use a pruning sealer (those can cause more trouble than anyone can imagine).
Once you have done that pruning, you can spread
compost around the drip line and or spread some Sea-90 around the same area, these two items will go far towards giving a boost to your trees.
The nuts are tasty, strong in flavor and oil content is pretty high too, if you have a mind for pressing oil from them, it goes for a nice sum of money per ounce.
Welcome to permies I know you will enjoy it here.