There are two different military discounts. There is the regular discount available at any ITR on post ( your brother would know what that is). He can purchase those tickets as a gift for you and anyone can use them.
Then, there is the 4 day Armed Forces Salute tickets. These are, by far, the least expensive better deal. However, while you can use them, the military member must be present. They are meant for the military member and their family. He could go with you on your vacation and purchase these for himself and for you. However, he can't purchase them just for your use like the discounted tickets at the ITR. The Salute tickets can be purchased at the gate and valid ID is required.
Does that make sense?