I have 3 old apple trees that could use some help. They are not in the best shape. They are vase shaped, about 25 feet tall, with about four main limbs. Each of these has exposed dead wood on the top side, running for many feet. There are dead branches here and there which I can prune out. There are a handful of water sprouts in each tree. I could top these to a lateral to force the growth outward. There is some crowded growth that could be thinned out. I want to keep the trees healthy, but I am concerned that too much pruning will put too much stress on trees that are already fighting decay. Any thoughts? The trees are in Maine.