Hi, I've got a beautiful tree line in my backyard with 35 year old evergreens that I love. Unfortunately, they seem to be dying from the bottom up, possibly drought? I'm not sure if I should remove a few to give them more space or if they are all dead. About 3 years ago, I trimmed all the lower branches that were touching the ground but none have grown back at all. I don't see a lot of sap on the trees either. Any advice for what to do is appreciated!

White Pine do not make lower branches because they are climax trees in a forest. Their canopy's are so dense, blocking so much sun in a white pine forest that not much can grow beneath them. There just isn't that much light available.
But all of those dead lower branches should be pruned back, flat and close to the trunk.
The same can be said for the blue spruce. Not a good deal of new branches can grow in poor sunlight. Blue spruce do best in full sun, new branches won't grow in poor light.
So they are not dying from drought, it is just what they do as they mature.