First of all, a big thank you to you!!
Now, as a Mom of a Marine, I have actually had experience with this. Buy the cheapest fare and hope for the best. In one case, my son's orders changed and we had to change his travel dates. Technically, we should have not been able to do so without penalty (it was not a military fare), but the agent was very nice when I explained the situation and let us change it.
On another occasion, I have to pay the difference in the fares and $100 change fee, but the fare difference was minimal, and we were still ahead from what we would have been if we had bought the military fare.
AA really does try to treat you guys right (way to go, AA!), so I would buy the cheap ticket and go from there.