Neither of you said where you are or what kind of situation your tree is in. It is very difficult to answer any questions without that information.
I never heard of pineapple broom so I looked it up. It is a tree that likes warm and dry, recommended to be grown in places like the American Southwest or Australia. In other places it is often grown against a sunny wall, to give it a warm, sheltered spot. it needs well drained soil. Once it is established it should not be watered too often, but you both have new trees that are still getting established.
Leaf dropping for your new trees could be just transplant shock. Otherwise it could be a reaction to too much cold. It is not hardy below USDA zone 7 and does not like cold winds.