When the leaves of an Italian Cypress tree thin out or turn brown from the bottom up, this is often a sign that the tree is suffering from stress, or from a lack of water. If there is still a part of your tree that remains green and lush, this is an encouraging sign as it means that the tree should eventually be able to pull through and recover.
You mentioned that your trees were planted only a few weeks ago and this could also be a factor contributing to their having developed brown leaves. Trees that are moved from a container into the soil can often experience what is known as transplant shock, one symptom of which is reduced growth.
TLC for your tree
To help your Italian Cypress recover, you may need to put in a little extra time and effort. One treatment would be to use a good root stimulator, coupled with some evergreen fertilizer: Both of which you should be able to source from any gardening specialist.
Another useful tip would be to take a PVC pipe, drill some holes into it, and plant it alongside the roots. This way you can place a hose directly into the pipe and this will allow you to deep-water the roots directly. With a little extra attention and perseverance, your Italian Cypress should be able to reach heights of up to 60 feet!