When I moved into my house 16 years ago, these evergreen trees were full and leafy almost from the ground up. They made a great privacy screen on our property line. Over the last 5 or so years, the branches have died back and lost their leaves slowly from the ground up the trees. They are now bare up about 6 feet or more. Plus there are some brown foliage among the green high in some of the trees. They are at least twice as tall as our two story house. The first photo is from my neighbor's yard looking towards our property and these trees in question. The second is on my side facing my neighbor's property. The third is a close up of the branches. Are they dying, or is this the natural progression of this type of tree (I don't know what it is)? Besides missing the screening aspect, I'm worried since they are planted right on the property line. I don't want them falling down into my neighbor's yard and causing damage. Do I need to remove them? Thanks!