Garland TX 7b-8a, I think.. : )

Why not send a sample of the trees in to your extension service for proper
diagnosis and treatment? Texas has an excellent extension service. And
if the trees are shading the house, that's a lot of free air conditioning
equivalent.

There are a lot of fungal leaf diseases in the world,
and trees mostly get along with them just fine. What's ailing your trees
may be one of those.

One of the easy things you could do to improve the health of the trees
is to remove the grass for a distance around the trees, to reduce the
competition between the grass and tree for water.