Why Are These Plants Dying
You have three different plant species showing dieback. This suggests that the problem is not a problem caused by insects or disease (which tend to be specialists somewhat), but rather cultural/environmental, what we call an abiotic problem.
It may be that the plants get a great deal of sun, plus reflected heat.
Could be too much water, or not enough water. Especially if the site is hot, the plants will need watering during dry spells. Get a rain gauge. There is no other way to know how much water your plants are getting or need.
Dwarf Alberta Spruce: They do not like it hot or dry. In that environment they get spider mites which brown out foliage. Here's is info about spider mites: https://extension.umd.edu/hgic/topics/spider-mites-trees-and-shrubs
Read "Monitoring" for how to know if they are an issue.
We see a lot of mulch in the photo. Mulch should never be piled on or even touch
the base of plants. That can cause disease and insect problems. Also, it should be kept to no more than 2-3" deep.
Here is a good fact sheet on abiotic plant problems: https://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/TreesandShrubs...