They are more simple than they look. Basically they wander around between random spots, with the enemies being biased towards te location of the server. If an opposing member is nearby or they get shoot they will stop and shoot at them. If the server is attacked the robots will go to the server and attempt to find the culprit. If low on health/ammo, they will go tho the nearest resupply box.
On the technical side they have a bunch of raycasts and an area that tells them the state of the world, and use them to modify variables. There is a variable for each input the player can make, and at the end the AI simply sends out the fake button presses it wishes to make. Overall it uses 259 lines of code and is probably horribly inefficent, but it works decently well.