We think that the browning out of the plant is caused by winter burn a.k.a. winter damage. This is the dessication/drying out of leaves in winter. Shallow-rooted, broad-leaved evergreens can be prone to this in certain conditions, especially if they go into the winter without enough hydration.
The injury occurs on dry, windy, warm, or sunny winter days when the ground is frozen. Plants are unable to move water from frozen soil to replace water lost from the leaves.
Leaves curl and droop, then brown from the tips and margins, giving the leaves a scorched appearance. In many cases, damage occurs during the winter months but symptoms appear in the spring as the plant begins to emerge from the winter dormant period and move into the spring growth phase.
Typically, damaged leaves fall off or are masked by new growth. Severely damaged shrubs may benefit from pruning. Prune to remove dead, damaged or broken branches and to stimulate new growth.

The spotted leaves are not a huge concern.
Given that the trees are not terribly old, be sure to water them when needed. This page can help:
https://extension.umd.edu/resource/watering-trees-and-shrubs


Christine

The first 18-24  months of establishment are important for long term health. Problems or plant death encountered during this time are often related to specimen, planting or after care issues. 
You may find clues within this planting page: 
https://extension.umd.edu/resource/planting-tree-or-shrub

If you plan to plant more to replace dead ones, we'd suggest planting native plants. This page will help with choices, and there is a link for a Maryland coupon for  new trees at the bottom:
https://extension.umd.edu/resource/tips-choosing-trees-and-shrubs


Christine