I think it is well possible and not the hardest thing to do. Sure its not easy, but its possible. The problem is knowledge. I've read 3 books about game AI and have some ideas how to do it. But you cannot just type it in a few words. So I will rather tell you, there are ways to do this, but you will have to learn a lot about game ai.
The idea is very good alredy. A stimulus, or trigger, or event, influences the soldiers. One important rule is, that the event makes it self known to all objects in the area of effect, and not that all objects query for events in their sourrounding. But I do not see player actions as a stimulus in that way. The player gives rather high level targets, like attack that enemy, move to that position. The AI must break it down into simple actions like fire a shot or move north 1 field.
Dynamic terrain and pathfinding, finding cover, acting as squad, everything is possible and has a lot of solutions.
I read the first three editions of AI Game Programming Wisdom, and they cover a lot of such stuff. But they arent exactly cheap. Quite some of the articles are also available freely in the web, but you have to find them.
If you have more specific problems or questions I can maybe give a better help.